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EXPERTS' EYE VIEW: Francisco Belda Maruenda Can the human eye detect an offside position during a football match? BMJ 2004; 329: 1470-1472 [Full text]

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Offside rule should be scrapped.

J. Geoff Taylor   (17 December 2004)

Four objects and one sound

Jonas Lofling   (17 December 2004)

Ballistic

George R Laking   (17 December 2004)

An old and unsubstantiated view on errors in judging offside

Raôul R. D. Oudejans, Frank C. Bakker, Peter J. Beek   (17 December 2004)

E viva Espana!

michael schapira   (17 December 2004)

Re: Offside rule should be scrapped.

Blair K Byrne   (18 December 2004)

One object/One sound

John R Allen   (18 December 2004)

Giving the Offside Rule the red card?

David A Sandler   (18 December 2004)

Re: One object/One sound

Michael G Carlston   (19 December 2004)

developing skill

Patrick M Simpson   (20 December 2004)

Human error or not?

David King   (20 December 2004)

When not to keep your eye on the ball

Thomas H Flynn, Alex J Shortt   (21 December 2004)

Linesmen make errors, but they are also biased

Kielan Yarrow   (21 December 2004)

At last a true science for the offside rule.

Yassin Nur   (22 December 2004)

Manchester United Excluded

Robert L. Boon   (22 December 2004)

Re: Manchester United Excluded

eamonn clarke   (23 December 2004)

Re: Manchester United Excluded

Michael S Jachuck   (23 December 2004)

Up the Arsenal

Michael O'Donnell   (23 December 2004)

An even more serious problem

Tiago Villanueva   (25 December 2004)

Re: An even more serious problem

Peter I Parry   (28 December 2004)

Re: Offside rule should be scrapped.

FRANCISCO BELDA MARUENDA   (13 January 2005)

Re: Four objects and one sound

FRANCISCO BELDA MARUENDA   (14 January 2005)

Re: Ballistic

FRANCISCO BELDA MARUENDA   (14 January 2005)

Re: An old and unsubstantiated view on errors in judging offside

FRANCISCO BELDA MARUENDA   (15 January 2005)

Re: Human error or not?

FRANCISCO BELDA MARUENDA   (15 January 2005)

Re: E viva Espana!

FRANCISCO BELDA MARUENDA   (17 January 2005)

Re: When not to keep your eye on the ball

FRANCISCO BELDA MARUENDA   (17 January 2005)

Re: Linesmen make errors, but they are also biased

FRANCISCO BELDA MARUENDA   (17 January 2005)

Four Eyes are Better than Two for Offside Decisions

Michael H HOYLE   (1 March 2005)

1 July 2006: Offside rule in football was modified substantially.

FRANCISCO BELDA MARUENDA   (20 March 2007)

Physical Laws, Ocular Neurophysiology and offside rule.

FRANCISCO BELDA MARUENDA   (20 March 2007)

Visual sequence in a game of offside in football.

FRANCISCO BELDA MARUENDA   (4 April 2007)

Which probabilities have referees and Assistant Referees of detecting an offside?

Francisco BELDA MARUENDA   (7 May 2007)

Physical laws and Offside Rule

Francisco BELDA MARUENDA   (9 May 2007)

Which criteria should the technological media follow to detect an offside?

Francisco BELDA MARUENDA   (25 May 2007)

IS IT POSSIBLE TO SPOT AND JUDGE AN OFFSIDE POSITION DURING A FOOTBALL MATCH?

Francisco BELDA MARUENDA   (28 May 2007)

Conclusions: Offside Rule versus Ocular Neurophysiology and Physical Laws

Francisco BELDA MARUENDA   (1 June 2007)

Offside rule should be scrapped. 17 December 2004
J. Geoff Taylor, GP Busselton Western Australia Send response to journal: Re: Offside rule should be scrapped.	Congratulations on your article. In the opinion of many observers, the Last World Cup series was ruined by all sorts of shonky rulings related to the offside rule. This rule can only be enforced reliably with the use of a third umpire, a road the football authorities have resisted going down. Hockey has already set a precendent - the offside rule should be scrapped. This would lead to much more exciting soccer. For a start we would almost certainly see more goals which after all is the objective of the game. Players enjoy scoring them and spectators enjoy seeing them. Perhaps we would see less violence from soccer fans off the field if their sides were at least scoring some goals on it. Competing interests: Nil
Four objects and one sound 17 December 2004
Jonas Lofling, Ph D Student Karolinska Institutet, S-14186 Stockholm Send response to journal: Re: Four objects and one sound	Dear SIR, I read with interest the article by Belda Maruenda about offside in football. The subject has been debated over the years, and it is not easy to make correct decisions according to the rule, as Belda Maruenda points out. I would first of all like to draw the attention to what I was taught at a course for referees in football. An experienced referee stressed the importance of trying not to look at the ball when it is going to be passed, but rather to listen to the sound, meaning you can then focus on the offensive players likely to be involved in the critical offside situation. That means you rather need to keep four objects in your visual field, and listening to the sound of the strike on the ball. Probably, this will not affect the conclusion drawn by Belda Maruenda. However, another thing I would like to point out is that it is crucial for the assistant referee to be in line with the players (Oudejans, R. R., Verheijen, R., Bakker, F. C., Gerrits, J. C., Steinbruckner, M., and Beek, P. J. (2000) Nature 404, 33) involved in the offside situtation, as is the case in fig. 2 in the paper of Belda Maruenda. This is most likely a bigger contribution to errors in the judging of offside. Anyway, these studies taken together, show the importance of the use of optical equipment, like cameras, in the assistance of the ruling of offside in football, i.e. if we want a correct decision, much like linesmen in tennis are helped nowadays. But perhaps we should accept the fact that humans are prone to making errors and see it as part of the game? Competing interests: None declared
Ballistic 17 December 2004
George R Laking, Centre Midfield Manchester Molecular Imaging Centre, Manchester M203LJ Send response to journal: Re: Ballistic	Hats off to Dr Maruenda for his dissection of this scientifically - and diplomatically - important issue. The eyes it seems just don't have the legs needed to keep up with the play, limping along like Achilles behind his tortoise. But hold on a minute! Those eyes are connected to one of the most sophisticated kinetic visual processing systems on the planet - the cerebral cortex. So perhaps, instead of looking at "offside" as a purely static rule, a more powerful explanation would show how it is inferred from the simultaneous cortical computation of a continually updated set of dynamic differential equations [1]. For the referee to call offside in this sense, is more a matter of ballistics. I encourage Dr Maruenda to advance his research in this direction. By comparing referees' calls with "gold standard" video data, it should be possible to predict the tolerances of referees' visual processing, and to learn about threshold conditions for "impossible" calls. Such research might even be fundable, assuming there is any commercial value in more efficient application of the rules. [1] Angelaki DE, Shaikh AG, Green AM, Dickman JD. Neurons compute internal models of the physical laws of motion. Nature. 2004 Jul 29;430(6999):560-4. Competing interests: Field Hockey Player (offside rule abolished in 2001)
An old and unsubstantiated view on errors in judging offside 17 December 2004
Raôul R. D. Oudejans, Lecturer, Institute for Fundamental and Clinical Human Movement Sciences Vrije Universiteit, 1081 BT Amsterdam, The Netherlands, Frank C. Bakker, Peter J. Beek Send response to journal: Re: An old and unsubstantiated view on errors in judging offside	Maruenda (2004) presents an interesting view on the inevitability of errors in judging offside in football. Unfortunately, Maruenda has missed recent scientific developments on this topic. The core of his hypothesis was already published in the Lancet in 1998 by his Spanish colleagues (Sanabria et al., 1998). These authors stated that in a potential offside situation players and ball may have changed position substantially in the time that eye movements are made by the assistant referee. Just as the contribution of Maruenda, the hypothesis by Sanabria et al. that errors in judging offside follow from the delay between seeing the pass and the relevant players was not corroborated with empirical evidence. Moreover, in an attempt to find this evidence Oudejans et al. (2000) were forced to reject this hypothesis. In their field experiment expert assistant referees, equipped with a miniature head-mounted camera, judged 200 played offside situations. The idea by Sanabria et al. (1998) could not account for the 40 errors that were made. Assistant referees already focused their gaze on the relevant players before the pass was made, implying that at the moment of passing shifts in gaze were no longer necessary. Instead the errors were consistent with the use of the optical angle between second last defender and receiving attacker, a variable that only veridically specifies who is closer to the defender’s goal line (attacker or defender) if the assistant referee is positioned on the offside line. However, Oudejans et al. (2000) also showed in their field experiment that the assistant referees were frequently positioned away from that line when they judged offside, occupying a point of observation from which errors are optically inevitable. In the same study this explanation was supported by error patterns in judging offside in 200 top matches obtained from television registrations. Thus, although intuitively appealing, the ideas by Sanabria et al. (1998) and Maruenda are unsubstantiated. The scientific evidence points to another explanation for most of the errors that are made in judging offside in Association Football. References Maruenda, F. B. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Oudejans, R.R.D., Verheijen, R., Bakker, F.C., Gerrits, J.C., Steinbrückner, M., & Beek, P.J. (2000). Errors in judging ‘offside’ in football. Nature, 404 (6773), 33. Sanabria, J., Cenjor, C., Márquez, F., Gutierrez, R., Martinez, D., & Prados-García, J.L. (1998). Oculomotor movements and football’s Law 11. The Lancet, 351, 268. Competing interests: None declared
E viva Espana! 17 December 2004
michael schapira, gastroenterologist jolimont hospital-7100 haine-st-paul belgium Send response to journal: Re: E viva Espana!	This is to my knowledge the second "serious" article published by a Spanish team on this subject.Six years ago Sanabria in the Lancet (1998,353,9170:2164) has already shown that human eye is incapable to distinguish "tight" offsides ("Oculomotor movements and football's law 11").It is urgent that the governing bodies of FIFA (INTERNATIONAL FEDERATION OF FOOTBALL) take into account such pertinent scientific informations, as the next world cup is just around the corner (june 2006). Competing interests: None declared
Re: Offside rule should be scrapped. 18 December 2004
Blair K Byrne, Referee/Undergraduate Student Douglas College - Sports Science Program Send response to journal: Re: Re: Offside rule should be scrapped.	I find the article quite interesting. I am currently taking the Sports Science program and this study I found to be particularly interesting. Having just learnt about the physiology of the eye, and as a referee this is a interesting study. However as a referee, no offside rule would actually be a detriment to the game in my opinion. All players would do is sit 20 yards behind the defenders, forcing the defenders to stay 20 yards farther back from the play. Pressure would be harder to maintain in the attacking end since the defense is no longer within a reasonable distance to put the ball back into the attacking third, maintaining the attack. The Kick and Run game would be then preferable and in my opinion makes for more interesting soccer. Also as a soccer goalie, the offside rule makes it so I as a goalie have a chance to make the saves that make the highlight reel. Competing interests: I am a soccer referee and goalie
One object/One sound 18 December 2004
John R Allen, Software Developer Medical applications Stanford University, California Send response to journal: Re: One object/One sound	If it was necessary to judge an offside offence in the way suggested by Belda Maruenda (focusing on five items simultaneously), indeed it would make arriving at a correct decision well-nigh impossible. Already Mr Lofling has pointed out, experienced linesmen are taught to listen for the sound when the ball is passed and at worst to pick up the movement of the striking of the ball with one's peripheral vision. In addition, the most important thing is that the linesman - assistant referee in the parlance of today - is constantly moving so as to keep parallel to the goal-line with the 'second-to-last' defender. In almost all cases this is the last defender as the goalie is normally some considerable distance away. If the AR does this, then it is only important to keep one's focus on that last defender. This way it is immediately apparent when an attacking player 'breaks' that line before the ball is played. The only time the AR should be level with and focusing on the ball is when the ball itself is the measure of offside. This is of course the case when the ball is 'past' the last defender and an attacking player has possession. Then the question is whether the attacking player receiving the ball is in front of the ball itself. If not, the player is onside. Again though the only focus for the assistant referee is on the 'line' of offside, in this case the ball. Everything else can be seen with peripheral vision. It is true that this is easier said than done, especially if you like football, because the natural inclination is to at least glance at the ball. However in terms of judging offsides this is not only unnecessary but will inevitably lead to wrong decisions. Thus I would suggest that the problem does not lie with the impossibility of focusing simultaneously on five separat actions. Rather the difficulty is in maintaining concentration, focus and 'keeping up with play' as we used to call it! Competing interests: None declared
Giving the Offside Rule the red card? 18 December 2004
David A Sandler, Consultant Cardiologist Royal Hospital, Calow, Chesterfield S44 5BL Send response to journal: Re: Giving the Offside Rule the red card?	What a helpful report this is. I get as angry as anyone when my team is penalised for "incorrect" offsides - both for and against. I accept that up in the stands, the field of view is somewhat wider, and thus we fans may assume we have a better chance of getting the call right. However, all the scientific reasons mentioned would still apply to us, many of us are older than the linesmen and our eyesight may not be as good, and my point is that whatever we fans think at the time, even we do not always get it right ourselves - and our view is bound to be coloured by our partiality. Maybe a trial of football without the offside rule would be an interesting experiment.... Competing interests: Supporter of Sheffield United who recently had a controversial goal disallowed incorrectly for "offside" on Saturday 11th December 2004 at Rotherham
Re: One object/One sound 19 December 2004
Michael G Carlston, Physician/Referee/USSF Referee Instructor 95403 Send response to journal: Re: Re: One object/One sound	This well-intentioned article suffers, perhaps terminally, from being outside the lines of real world conditions. As pointed out by two prior commentators, experienced referees quickly learn that in any highly competitive game from 16 year old boys upwards, it is impossible to simultaneously watch the ball and defenders positioning so you must listen for the strike of the ball. Errors do occur and this effort to more carefully examine the physiologic and perceptual constraints is a worthy addition to the discussion however, more real world investigation like Oudejans effort rather than theoretical speculations are needed. The studies of assistant referee positioning show significant malpositioning to be the norm with top professional ARs averaging 2m from correct position (3m in the third of the field closest to the goal) and mean maximal distance of 7m (also greater still in that crucial final 1/3). As any assistant referee knows from simply looking down the touchline to determine if the ball is in or out of play, looking 60-70m across an unlined field through a number of rapidly moving bodies, even 2m can deceive. Another question is how inaccurate is the traditional method of listening for the ball strike while the assistant referee attempts to keep his/her trailing shoulder inline with the second to last defender? Sounds travels slower than light, Consideration of time for the sound to travel, processessing of that auditory information and movement of the players during that time span would then need to be considered. Oudejans RR, Verheijen R, Bakker FC, Gerrits JC, Steinbruckner M, Beek PJ. Errors in judging 'offside' in football. Nature. 2000 Mar 2;404(6773):33. Krustrup P, Mohr M, Bangsbo J. Activity profile and physiological demands of top-class soccer assistant refereeing in relation to training status. J Sports Sci. 2002 Nov;20(11):861-71 Competing interests: None declared
developing skill 20 December 2004
Patrick M Simpson, administrator Walon UK Ltd., OX25 5HB, United Kingdom Send response to journal: Re: developing skill	If Maruenda's points about the capabilities of the eye & brain are correct, won't they apply to players as much as officials ? In that case, how can it be possible to play tennis doubles ? Tennis players would each have to judge the movements of three other players, keep their eye on the ball, and aim their shot. Likewise, many football players possess a positional awareness that allows them to track the movements of colleagues and opponents, as well as the ball. I've no idea how its done, but its manifestly true every time one sees a player make an outstanding pass, or intercept one. They are clearly capable of following the movements of five or more objects. Why is it impossible for referees and their assistants to develop similar skills ? As to the call for use of video replays, I suggest an unconventional alternative. Ban video replays altogether. That would put fans (especially viewers) in the same position as the officials. After all, what did we do in the days before television, and what do we do at untelevised matches ? Of course, offside calls are a difficult task, but this is recognised in the laws of the game. The rules state that the referee's decision is final, and assistant referees are instructed to give the benefit of the doubt to attacking players. These tacitly accept the existence of uncertainties and errors of judgement, and indicate that they are something we just have to live with. Competing interests: None declared
Human error or not? 20 December 2004
David King, FA Licensed Instructor York YO32 9XW Send response to journal: Re: Human error or not?	The peripheral vision of the eyes for Assistant Referees (AR) is very wide. The AR can see and hear the ball being kicked and maintains a line parallel to the second rear-most defender. Therefore, providing the AR is exactly parallel at all times a sound judgement can be made. The AR is concentrating on one moving object (the second rear-most defender in most instances and is using this for the basis of any offside decision. The ball is not a fixation point but this defender. It has already been sugggested that sound of the ball being kicked is of paramount importance also. I would suggest that in 99% of cases that the AR makes a correct judgement, based upon the law. The prime decision is whether the player in an offside position is in fact involved in active play. Apart from professional / senior games most matches are officiated by a referee only with no neutral AR. In these circumstances it is impossible for the referee to give an absolute decision in open play (different for free kicks). The referee has to use his judgement (pitch marking and grass cutting marks are helpful) in applying Law 11 to the best of his ability. David King FA Licensed Instructor York, England Competing interests: None declared
When not to keep your eye on the ball 21 December 2004
Thomas H Flynn, Ophthalmologist Institute of Ophthalmology, London EC1V 9EL, Alex J Shortt Send response to journal: Re: When not to keep your eye on the ball	We believe that Maruenda’s conclusion that the human eye cannot detect offside in football is incorrect for the following reasons: Firstly, his assertion that “the minimum time needed to detect the three players relevant to the offside position is 160 ms” is based on the false premise that a linesman needs to move his head or eyes in order to detect the positions of the ball and relevant players. This is not necessarily the case. The normal visual field extends beyond 90 degrees on the temporal side. Therefore, a linesman with normal visual fields, standing on the touchline, and facing infield, will have all 22 players within his visual field at all times. Secondly, the linesman does not need to focus on 5 separate objects simultaneously (this is actually impossible) in order to apply the offside rule. In most cases the goalkeeper is so far away from the other players that it is easy to identify the second-last defender. Assuming the linesman stays in line with this player then he has to determine only 2 things simultaneously: 1. The position of the foremost attacking player relative to the 2nd last defender. 2. The timing of the pass. Based on the fact that the human eye has evolved to possess different types of visual acuity for different visual tasks, we believe that it is indeed possible to perceive these two separate events simultaneously. Each of these events has a different requirement in terms of visual acuity. The level of acuity required to detect the presence of a moving target (minimum visible) is much less than that required to locate the features of a target relative to each other (minimum discriminable/ vernier acuity). Whilst visual acuity is highest at the central retina (fovea centralis) and falls with increasing retinal eccentricity, the peripheral retina is relatively specialised for motion detection. Hence, by using central vision to discern the relative position of the foremost attacking player to the 2nd last defender and peripheral vision to detect the change in velocity/ direction of the ball at the moment it is passed, it is possible for the human eye to detect an offside position. Competing interests: None declared
Linesmen make errors, but they are also biased 21 December 2004
Kielan Yarrow, Post-doc researcher Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR Send response to journal: Re: Linesmen make errors, but they are also biased	For the last few years I have been running experiments investigating how we perceive the timing of events when we move our eyes. Predictably enough, it was a Brazilian who first pointed out that my research might explain why linesmen sometimes make dubious offside decisions. I became quite excited about the possibility of being cited by Des Lynam. In fact, I probably would have written something on the subject and ended up making the same mistakes as Maruenda does, had I not first come across Oudejans et al.’s work. If linesmen did what Maruenda suggests they do, his analysis would need to be supplemented to include various biases that affect our judgements about spatial position and temporal order around the time we move our eyes (e.g. Schlag & Schlag-Rey, Nature Reviews Neuroscience, 2002, 3, 191-215). Unfortunately, Maruenda seems to be analysing the wrong perceptual problem. As previous contributors have mentioned, linesmen are told to look at (and remain in line with) the last but one defender, so no saccade is required. Whether linesmen actually do this of course is a matter of debate. Oudejans et al. have the best data, but it is based on a head mounted camera, a rather inexact measure of where the eyes are pointing. However, even if linesmen are in the correct position, doing as they are told, this doesn’t solve all the problems. When we report the location of a moving object at the precise time another event occurs, our judgments are systematically biased (the “flash-lag” effect). This illusion has been explicitly related to the offside problem (Baldo et al., Perception, 2002, 31, 1205-1210). Using the sound of the pass rather than peripheral vision to estimate when the ball is struck introduces additional problems. Observers show idiosyncratic biases when judging whether auditory and visual events co-occur. When you consider all the biases that affect perceptual judgements, it’s impressive that linesmen ever get it right at all. But then the rich visual environment of the football match is a long way removed from the austere testing room of the psychophysicist, which is presumably why football is so much more enjoyable than science. Competing interests: None declared
At last a true science for the offside rule. 22 December 2004
Yassin Nur, staff grade coventry pct, sexual health clinic, Stoney stanton road, coventry, C1 4FH Send response to journal: Re: At last a true science for the offside rule.	How many will suffer again and again because of the subjective interpretation of the referees. I feel really sorry for them for the abuse they had from managers as well as from players and supporters like me. It is time to introduce computers to help them after all a computer is faster than the 4th referee and it will probably cost less and better for those of as who suffer from hypertension. Competing interests: None declared
Manchester United Excluded 22 December 2004
Robert L. Boon, Paediatric Consultant Musgrove Park Hospital, Taunton TA! 5DA Send response to journal: Re: Manchester United Excluded	Dear Sir, The authors of this article need to be aware that although their research is true for the normal human eye - there is an exception. Anyone who follows the Premiership in the U.K. will attest to the fact that Sir Alex Ferguson and all the Manchester United players are able to correctly call an offside position no matter where they happen to be on the pitch. Yours Sincerely, Dr.Robert Boon Competing interests: Lifelong Liverpool Fan
Re: Manchester United Excluded 23 December 2004
eamonn clarke, gp cambs Send response to journal: Re: Re: Manchester United Excluded	We should also note the corollary of the Man United phenomenon: that Arsene Wenger the Arsenal manager will be unlikely to spot any offside violations as he so very rarely manages to "see the incident". Competing interests: None declared
Re: Manchester United Excluded 23 December 2004
Michael S Jachuck, Clinical Fellow in Cardiology Wansbeck General Hospital, Ashington, Northumberland, NE63 9JJ. Send response to journal: Re: Re: Manchester United Excluded	Following on from Dr. Boon's comments, the authors may also wish to consider the influence of environmental and geographical factors on basic human eye physiology. This is demonstrated regularly by the obvious variations between offside decisions favouring the home team at Old Trafford, Manchester compared with matches played at other stadia in England. It has been suggested that this phenomenon could be related to the peculiar temporal flux that exists around the same venue whereby time itself appears to slow allowing longer periods of injury time to be played until Manchester United have scored the winning goal (which was probably offside anyway). Competing interests: Long suffering and very bitter Newcastle United supporter
Up the Arsenal 23 December 2004
Michael O'Donnell, Loiterer Loxhill GU8 4BD Send response to journal: Re: Up the Arsenal	This paper ignores one significant influence on decisions made by linesmen – I beg their pardon, assistant referees – when one of London’s lesser clubs is playing. Arsenal players are experts at “winning” offside decisions with well drilled body language. So skilled have they become that earlier this season a referee admitted that their body language had persuaded him not to give a penalty against them. But then as supporters of other Premiership sides know, often to their cost, Arsenal players always insist on refereeing the game as well as playing it. Michael O'Donnell michael@odonnell99.freeserve.co.uk Competing interests: One-time supporter of Doncaster Rovers
An even more serious problem 25 December 2004
Tiago Villanueva, Final year medical student University of Lisbon, Av. Professor Egas Moniz, 149-028, Lisbon, Portugal Send response to journal: Re: An even more serious problem	I think it it would be a significant accomplishment to use optical technology in football matches. Its role is not restricted to a mere gold standard in confirming an offside call made by the referee, but also important in disciplinary situations where one player injures another intentionally, and the referee does not see it. Moreover, football is a corrupt world, and technology could go a long way in neutralizing any attempts of bribery or match fixing. That's even more important than pinpointing an offside call accurately. It's about enforcing a clampdown on a highly prevalent social cancer, corruption in football. Competing interests: None declared
Re: An even more serious problem 28 December 2004
Peter I Parry, consultant psychiatrist Eastern CAMHS, Paradise, Adelaide, South Australia 5075 Send response to journal: Re: Re: An even more serious problem	It is amusing to read a paper such as Maruenda's during the holiday season, but given the passion with which some people take their football, it does have a serious side. Media reports suggest lives may literally be at stake over controversial decisions - those of referees and also fans - either with cardiac conditions or at risk of hooliganism from other fans. The potential for corruption is another problem. Given calls from some readers to scrap the offside rule, readers may be interested in the rules from two other football codes - Australian rules football is a high scoring game that manages with no offside rule at all, and secondly Gaelic football in Ireland (a code very similar to soccer but players can make hand contact with the ball) has an offside rule pertainable only to the small goalkeeper's box. Infringements by strikers for the attacking team entering the small goalkeeper's box prior to the ball are officiated by linesmen ("goal umpires") standing beside the goal: A situation which would seem, if not free from error, then less open to error than detecting the ball and multiple player movements over a wider and deeper visual field as in soccer. Perhaps after 80 years the offside rule in soccer is due for a major overhaul? Competing interests: former player and coach of Australian rules football and player of Gaelic football
Re: Offside rule should be scrapped. 13 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R Fernández Miñarro, No 1, Alquerías, 30580, Murcia, Spain Send response to journal: Re: Re: Offside rule should be scrapped.	I think that maybe you have not fully understood my paper. It concludes saying that nobody is able to see an offside: nor the referee, nor the assistant referee, nor the public or the people watching the match on TV. There is just one situation nowadays in which we can surely affirm that there is or not an offside position. I am referring to using freeze frame television “just in the precise moment when the ball is being passed” and frame by frame analysis. References Belda Maruenda, F.(2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Re: Four objects and one sound 14 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R Fernández Miñarro, No 1, Alquerías, 30580, Murcia, Spain Send response to journal: Re: Re: Four objects and one sound	Assistant referees, empirically, were the first who detected the human incapability of applying correctly the offside rule. Later on, they developed empirical techniques to solve this physiological lack. This is a method error, because the speed of sound is slower than the speed of light (the image of the players in the retina). So three situations can take place: - First, it is very probable that in a premier or second league matches, in the case of national teams or Champions League, with the noise of the stadium, the noise when the ball is touched can be hard to listen to; - Secondly, although there were no spectators, the touch of the ball can be so soft that it is impossible to hear it; - Thirdly, in the case that the noise of the ball being touched is heard, the assistant referee can see the forward player running to the goal line of the opposite team and the defender running to the centre of the pitch. It means that he will never know what the original position was when the pass took place, because the speed of sound is slower than the speed of light. So, when he would receive the sound stimulus, the players would have moved in the pitch. The first situation that I expose in my research is quite clear. If all the players that take part in an offside are not within the visual field, it is obvious that the move cannot be judged or applied. From the research made by Oudejans et al. (2000), we can understand that, in order to detect exactly an offside nowadays, a television camera has to be focusing to the penultimate defender with an angle of 0º, because if the camera would be located with an angle of 1º before of after the player, that would lead us to visual errors of perception. References Belda Maruenda, F.(2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Oudejans, R.R.D., Verheijen, R., Bakker, F.C., Gerrits, J.C., Steinbrückner, M., & Beek, P.J. (2000). Errors in judging ‘offside’ in football. Nature, 404 (6773), 33. Competing interests: None declared
Re: Ballistic 14 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R Fernández Miñarro, No 1, Alquerías, 30580, Murcia, Spain Send response to journal: Re: Re: Ballistic	The latency period for a saccadic movement is of 200ms. But a person trained to develop those movements, as football referees and assistant referees, can do them in a shorter period. This is even clearer when they know that in a given situation they have to do several saccadic movements (one following the other), so that they can use even less time to develop them. The Central Nervous System can process at the same time information from different mobile objects (different football players moving at the same time). The human eye can store and integrate that information more precisely, obtaining a shorter Latency Period (130ms) and the speed of the saccadic movements to locate the different players would be the minimum (10ms) in a range that goes from 10 to 80ms depending in the angle between both players. This gives us a minimum amount of time of 160ms in order to detect all the players that participate in an offside game, because the three saccadic movements have to be developed. References Belda Maruenda, F. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Re: An old and unsubstantiated view on errors in judging offside 15 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R. Fernández Miñarro, Nº 1, Alquerías, 30580, Murcia, Spain. Send response to journal: Re: Re: An old and unsubstantiated view on errors in judging offside	The present research made by Belda Maruenda, F. (2004. Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472), contains seven new and outstanding features that make it different from the study of Sanabria et al., (1998. Oculomotor movements and football’s Law 11. The Lancet, 351, 268). These features are the following: 1. The research starts from the controversy: The introduction of the Offside Rule in 1866 (XIXth century), a period in which the physiology of the eye ordered to make the function that detects correctly the offside was unknown. 2. In the study carried out by Sanabria et al., they don't pay attention to the most important element: the ball. Five different objects participate in a game (two attackers, two defenders and the ball), if it is an ideal game, because in most of the games there are more than four players that the referee must have located before the ball is passed. 3. The Central Nervous System takes part in order to process all the information that the eye receives and to be able to give the necessary stimulate so that the eye can perform its movements (above all saccadic movements) and the accommodation. This influences in the Period of Latency of the saccadic movements (it goes from 200ms to 130ms). The latency period for a saccadic movement is of 200ms. But a person trained to develop those movements, as football referees and assistant referees, can do them in a shorter period. This is even clearer when they know that in a given situation they have to do several saccadic movements (one following the other), so that they can use even less time to develop them. The Central Nervous System can process at the same time information from different mobile objects (different football players moving at the same time). The human eye can store and integrate that information more precisely, obtaining a shorter Latency Period (130ms) and the speed of the saccadic movements to locate the different players would be the minimum (10ms) in a range that goes from 10 to 80ms depending in the angle between both players. This gives us a minimum amount of time of 160ms in order to detect all the players that participate in an offside game, because the three saccadic movements have to be developed. 4. The time that the eye needs to detect all the objects is the sum of the integration of the eye movements and the accommodation that it has to do. All the eye movements are carried out at the same time. But, if there is to make saccadic movements more smooth pursuit movements or vergence movements, aside from integrating these movements, it is necessary to add them. If there is also eye accommodation, the time needed to carry it out is longer than the eye movements, so the time needed would be that of accommodation. 5. Calculus of the minimum amount of time to locate all the players that take part in an offside. The best situation is of 160ms: just the saccadic movements are carried out plus the latency period, both of them in the minimum amount of time, as I have already said. 6. There are three situations that can take place in an offside: A) If all the players that take part in an offside are not within the visual field of the Referee, the Assistant Referee or the spectators, it is obvious that an offside position could never be detected. It is a strange situation for the assistant referee, but it is possible. B) The best situation: All the players are located inside the visual field and, even better, there would just be the need of carrying out saccadic movements. C) Accommodation: If there are players located less than six metres away from the Referee or the Assistant Referee and other players more than six metres away, the human eye has to start the eye accommodation mechanism. That would imply much more time. 7. It concludes with: Referee's errors. An error means carrying out incorrectly or making a mistake in an action we are physiologically prepared for. The study of Belda Maruenda, F. concludes with the human eye's and the Central Nervous System's physiological incapability to detect an offside just in the moment when the ball is being passed. It is necessary to know the exact position of the players in that precise moment. Revising the eye physiology, it is scientific evidence that no human being, without the aid of modern technology, can carry out that function. Insisting on the study of Belda Maruenda, F. it is precise to know that inside the visual field, taking into account that there were several objects (players), there is just one Fixation Point: the object (player) that is located in the fovea. And the eye, in order to change the fixation point (object/player) has to carry out saccadic movements to locate those objects/players in the fovea. It has to be taken into account that the saccadic movements can be broken out voluntarily or intentional when the fixation point changes to look at another object/player. But, they can also break out involuntarily or unintentionally when an object enters in the visual field or when a movement is detected in the peripheral retina; in this case a saccadic movement also has to start if we want to know the geographical location of that object/player exactly. In this case, the object/player will pass from the peripheral retina to the fovea (saccadic movement). Affirming and insisting that there is no need of starting eye movements, not even accomodation, to detect an offside in football, is against the present knowledge about eye physiology and the Central Nervous System. It would be an important scientific step in the research on eye physiology to demonstrate in a scientific piece of research that there is no need to start a saccadic movement to look from an object/player to another within the visual field. If that would be demonstrated, all medical texts about physiology of the oculomotor system should be changed and the students of medicine would be grateful. I encourage Oudejans et al. other scientists to start that research. It is an exciting challenge and all the doctors would be very grateful. However, it is important to admit that from the research by Oudejans et al. (2000) we can draw that to detect an offside exactly nowadays, a television camera has to be focusing to the penultimate defender, in an angle of 0º, because if it focused 1º before or after, that would lead us to visual errors of perception. References Maruenda, F. B. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Oudejans, R.R.D., Verheijen, R., Bakker, F.C., Gerrits, J.C., Steinbrückner, M., & Beek, P.J. (2000). Errors in judging ‘offside’ in football. Nature, 404 (6773), 33. Sanabria, J., Cenjor, C., Márquez, F., Gutierrez, R., Martinez, D., & Prados-García, J.L. (1998). Oculomotor movements and football’s Law 11. The Lancet, 351, 268. Competing interests: None declared
Re: Human error or not? 15 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R. Fernández Miñarro, Nº 1, Alquerías, 30580, Murcia, Spain. Send response to journal: Re: Re: Human error or not?	Insisting on the study of Belda Maruenda, F. it is precise to know that inside the visual field, taking into account that there were several objects (players), there is just one Fixation Point: the object (player) that is located in the fovea. And the eye, in order to change the fixation point (object/player) has to carry out saccadic movements to locate those objects/players in the fovea. It has to be taken into account that the saccadic movements can be broken out voluntarily or intentional when the fixation point changes to look at another object/player. But, they can also break out involuntarily or unintentionally when an object enters in the visual field or when a movement is detected in the peripheral retina; in this case a saccadic movement also has to start if we want to know the geographical location of that object/player exactly. In this case, the object/player will pass from the peripheral retina to the fovea (saccadic movement). Affirming and insisting that there is no need of starting eye movements, not even accomodation, to detect an offside in football, is against the present knowledge about eye physiology and the Central Nervous System. Assistant referees, empirically, were the first who detected the human incapability of applying correctly the offside rule. Later on, they developed empirical techniques to solve this physiological lack. This is a method error, because the speed of sound is slower than the speed of light (the image of the players in the retina). So three situations can take place: First, it is very probable that in a premier or second league matches, in the case of national teams or Champions League, with the noise of the stadium, the noise when the ball is touched can be hard to listen to; Secondly, although there were no spectators, the touch of the ball can be so soft that it is impossible to hear it; Thirdly, in the case that the noise of the ball being touched is heard, the assistant referee can see the forward player running to the goal line of the opposite team and the defender running to the centre of the pitch. It means that he will never know what the original position was when the pass took place, because the speed of sound is slower than the speed of light. So, when he would receive the sound stimulus, the players would have moved in the pitch. The first situation that I expose in my research is quite clear. If all the players that take part in an offside are not within the visual field, it is obvious that the move cannot be judged or applied. References Maruenda, F. B. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Re: E viva Espana! 17 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R. Fernández Miñarro, Nº 1, Alquerías, 30580, Murcia, Spain. Send response to journal: Re: Re: E viva Espana!	The FIFA has a serious problem, It is an autonomous entity and they do not take into account the scientific research and they forget about it, because since the 18 december, they have had time enough to make a decision, something that has not happened up to now. The history of science shows us that, sometimes, big scientific discoveries had to wait a few years to be taken into account. There is no doubt that, this time, the research will be taken into account in the future. We cannot avoid scientific advance. References Belda Maruenda, F. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Re: When not to keep your eye on the ball 17 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R. Fernández Miñarro, Nº 1, Alquerías, 30580, Murcia, Spain. Send response to journal: Re: Re: When not to keep your eye on the ball	Insisting on the study of Belda Maruenda, F. it is precise to know that inside the visual field, taking into account that there were several objects (players), there is just one Fixation Point: the object (player) that is located in the fovea. And the eye, in order to change the fixation point (object/player) has to carry out saccadic movements to locate those objects/players in the fovea. It has to be taken into account that the saccadic movements can be broken out voluntarily or deliberately when the fixation point changes to look at another object/player. But, they can also break out involuntarily or unintentionally when an object enters in the visual field or when a movement is detected in the peripheral retina; in this case a saccadic movement also has to start if we want to know the geographical location of that object/player exactly. In this case, the object/player will pass from the peripheral retina to the fovea (saccadic movement). Affirming and insisting that there is no need of starting eye movements, not even accommodation, to detect an offside in football, is against the present knowledge about eye physiology and the Central Nervous System. It would be an important scientific step in the research on eye physiology to demonstrate in a scientific piece of research that there is no need to start a saccadic movement to look from an object/player to another within the visual field. If that would be demonstrated, all medical texts about physiology of the oculomotor system should be changed and the students of medicine would be grateful. During my research, I lost several years studying the physiology of visual acuity, until I got to the conclusion that it had no function applied to the offside rule. It just takes part from the point of view of seeing better (without glasses) or worse (wearing glasses or contact lenses). The offside rule requires watching at five different objects (two attackers, two defenders and the ball). Sometimes, the goalkeeper leaves the goal and two defenders take part in the game of offside, not the goalkeeper. References Belda Maruenda, F. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Re: Linesmen make errors, but they are also biased 17 January 2005
FRANCISCO BELDA MARUENDA, specialist in family medicine (general practice) Centro de Salud de Alquerías, C/ R. Fernández Miñarro, Nº 1, Alquerías, 30580, Murcia, Spain. Send response to journal: Re: Re: Linesmen make errors, but they are also biased	Thank you for your comments about my paper. But, I affirm that your opinion is mistaken. You say that the assistant referee is at the same level as the penultimate defender, when he thinks that there is a defender in an offside position if he would be passed the ball, and in this case, no saccadic movement would be needed. This is not correct, because if the assistant referee looks at the player that has the ball (fixation point), he cannot locate the penultimate defender, and he could move. That is why, when the ball is passed, the assistant referee has to carry out a saccadic movement to locate the forward who will receive the ball, another movement to locate the penultimate defender and a third saccadic movement to locate the goalkeeper (or the last defender, if there are two defenders behind the goalkeeper). It is a challenge for science and for the physiology of the oculomotor system to demonstrate that there is no need to carry out any saccadic movement. If this would be the case, it would be an extremely important scientific discovery. I encourage the researchers interested in the physiology of the oculomotor system to start researches to demonstrate that, although in my opinion the failure is secure. With the "flash-lag" effect, if we look straight to an object, we can follow another object moving with the peripheral vision of the retina, because both of them are inside the visual field. But the problem of the offside rule is that we need to know the exact geographical location of several players when the ball is being passed. Physiologically, for that movement, a saccadic movement has to be carried out for each object/player that has to be located. As all the players are moving, there is a physiological incapability to apply/judge correctly an offside. References Belda Maruenda, F. (2004). Can the human eye detect an offside position during a football match?. Britisch Medical Journal, 329, 18 December, 1470 -1472. Competing interests: None declared
Four Eyes are Better than Two for Offside Decisions 1 March 2005
Michael H HOYLE, Managemeent Consultant RG25 2 RH Send response to journal: Re: Four Eyes are Better than Two for Offside Decisions	In his paper “Can the human eye detect an offside position during a football match?” Francisco Belda Maruenda concluded that it is beyond the capacity of the referee’s two human eyes to keep in his visual field at least five objects at the same time – the two players of the attacking team, the last two players of the defending team, and the ball. In this way, he provides an explanation for the relatively high proportion of “bad” offside decisions detected by the television analysts. He suggests that the use of modern technology is required to limit these errors. I would like to suggest an alternative approach using the same number of officials but based on the combined workings of four eyes and not just two. New Proposal My starting point is that to be offside requires all of three criteria to be met: 1. At the time when the ball was last played by an attacking player, at least one attacking player is in an offside position (“timing”) 2. At least one attacking player is nearer the defender’s goal line than at least two defending players (“position”) 3. At least one attacking player in an offside position is “actively involved” with the play (“interfering”). Under the present method of implementing the offside rule, the assistant referee (linesman) raises his flag when he considers all three criteria met. The referee will take the judgement of the assistant referee into consideration as well as his own before deciding whether to blow his whistle and give an (indirect) free kick for offside, or not . In my view it would be more satisfactory and lead to a higher proportion of correct decisions to let the assistant referee make the decisions regarding “position” and “interfering”, and leave it to the referee to decide on “timing”. The assistant referee would raise his flag when there were less than two defenders between the most advanced attacker and the goal line. Where the ball is, who plays it and to whom it is passed is irrelevant in deciding what the assistant referee does. The referee is following the ball and when he sees the attacker about to, and actually kick, the ball he looks up to the assistant referee: - If the flag was up, is up and stays up, the referee blows his whistle for offside. - If the flag was up and was coming down after the ball was played, the whistle is blown. A defender or an attacker (or both) have almost certainly moved back after the ball was played. - If the flag was down but is raised as and after the ball is kicked, the referee does not blow for offside. The attacker has most probably broken through to be in an offside position after the ball was played. - If the flag was down and stays down then clearly there is no whistle. In this revised approach, the referee’s eyes need to focus on just the flag and the ball/passer’s boot. The assistant referee has to focus on the position of one man relative to two others (generally this is a single defender as the goalkeeper is the second defender). Analysis From the attacking side’s point of view, they do not want their attacker A1 in the following position to be assessed as being goal side of defender D2 at the time the ball is kicked when in reality he was not. In the new approach to implementing the offside law, the referee (R), aware of the possibility of an offside is monitoring A2, the ball and the assistant referee (L). As I understand Maruenda (2005) , the delay between seeing the ball kicked by A2 (in the general direction of A1) is only 140ms because the latency penalty is not applicable. The referee then looks in the direction of the linesman and sees the position and motion of the flag – a saccadic movement taking, say, 200ms. That is a total of 340ms before he makes his decision. During this time L has observed the relative position of A1 and D2, taking 140 ms, and moved his flag appropriately, after say 100ms; this gives a total of 240ms before the R can correctly know A1’s “offside status”. So in this example and on these assumptions, what R sees is the “offside position” only 140ms after A2 became offside at a time 100ms (= 340-240ms) after the ball was kicked, considerably less than the times quoted in Maruenda (e.g. 500 - 600ms). In fact this 100ms is the difference between the time it takes for R to see L after the ball was kicked, and the response time of the L in raising his flag. In this example it has been implicitly assumed that L is quicker than the R, but he might be much slower and this could result in a wrong decision (R eyes would see the flag down). Conclusion If these the response times of the two officials were small and of comparable magnitude (which seems a not unreasonable expectation given training and practice) the decision of the referee would be taken in much the same time frame as in a normal incident, for example, a possible late the tackle. The analysis suggests that the error rate on offside decisions would be substantially reduced by the new approach. As a long term football supporter (and especially of Arsenal) this would be very much welcomed! An additional advantage is that all the players on the field would know the current judgement of the assistant referees regarding the position of the lead attackers. This should lead to fewer stoppages for offside, adding to the continuity of play. It would help real time communication between the players and officials, which in football is noticeably absent – unlike rugby where the referee does advise players in key situations to take remedial action or take the consequnces. Competing interests: None declared
1 July 2006: Offside rule in football was modified substantially. 20 March 2007
FRANCISCO BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: 1 July 2006: Offside rule in football was modified substantially.	On 1 July 2006 the new Laws of the Game -1- (IFAB, 2006), modified at the 119th International Football Association Board (IFAB) meeting in London, England on 26 February 2005, comes into force. Offside rule in football (soccer in USA) was modified substantially. Now, the key factor in this rule application is that the player must be in the offside position (Fig. 1) exactly in the moment when the ball is passed from one of his team mates, not when he receives the ball or when the ball is en route between the players. Moreover, it is not an offence in itself to be in an offside position. A player in this position is penalised only if he is, according to the referee, involved in active play by interfering with play, interfering with an opponent, or gaining an advantage by being in that position. Offside errors -2,3,4- in football are very frequent, but: the human eye and the brain are enabled physiologically to spot and judge an offside in football? At the present time, there are several companies of modern technology in the world that are investigating technological media to detect an offside in football in real time. References 1. International Football Association Board. New Laws of the game. Zurich: Fédération Internationale de Football Association (FIFA), 2006. http://www.fifa.com/en/regulations/regulation/0,1584,3,00.html 2. Helsen W, Bilis B, Weston M. Errors in judging "offside" in association football: test of the optical error versus the perceptual flash-lag hypothesis. J Sports Sci. 2006 May;24(5):521-8. 3. Baldo MV, Ranvaud RD, Morya E. Flag errors in football games: the flash-lag effect brought to real life.Perception. 2002;31(10):1205-10. 4. Oudejans RR, Verheijen R, Bakker FC, Gerrits JC, Steinbruckner M, Beek PJ. Errors in judging 'offside' in football. Nature. 2000 Mar 2;404(6773):33. Competing interests: None declared
Physical Laws, Ocular Neurophysiology and offside rule. 20 March 2007
FRANCISCO BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Physical Laws, Ocular Neurophysiology and offside rule.	In order to detect an offside in real time, without possibility of physiological or technological error, the current text of the Offside Rule demands the active participation some Physical Laws and all the present knowledge on Ocular Neurophysiology. PHYSICAL LAWS AND OFFSIDE RULE The offside rule is directly related to some physical concepts: speed, space, time and acceleration. The human eye needs time to carry out the eye movements; players run at a different speed and they cover different spaces in the playing field as the eye tries to locate the exact position that those players had in the field "in the precise moment when the player who has the ball passes it". The acceleration in each players' race allows them to run a specific space in the pitch in some second tenths. OCULAR NEUROPHYSIOLOGY AND OFFSIDE RULE The peripheral retina gathers information that the brain uses to program the eye movements, basically from the parafoveal area -1,2,3-. In a football match the saccadic eye movements are those used between two players, to look at each other. In the offside, saccades are used when the ball has already been passed, to locate all the players that take part in a game (if they are all within the visual field). A saccadic movement needs time that depends on the latency -4- (duration 80-135 miliseconds) and duration of the saccadic movement -5,6- (between 30 and 100 msec: A 40º saccade -6- requires 110 msec, 40 msec for 7'5º and 30 msec for 2º saccade -7-). The cognitive process to acquire and to process all the visual information of the object in the visual field and to decide which is the following object of interest is performed during ocular fixation -8-. The duration of ocular fixation can be extremely brief -9-: about 40 or even 30 msec. Eye accommodation is the capacity that the eye has to focus. Within the visual field, when we want to change the fixation point from a far object to another one located at less than 6 metres from us, the crystalline changes its convexity -10-. Normal latency as well as duration appear to have a large interindividual variability -11-. The normal response latency is of 394 ms (± 46 SD). In order to change the focus from a far to a close object, 640msec. are needed, and viceversa (from a close to a far object), it takes 560ms -12,13-. In an Offside game, if there are players located further than 6 meters away from the Referee or the AR and other players located at less than 6 metres, they have to carry out the Eye Accommodation. When the eye moves, several anatomical structures of the human brain -14,15- take part. The function of these structures is to process at the same time -9,16- all the information gathered during the fixations -8-, store it -17- and integrate it, as well as to program the following eye movements -18-. The combined presentation of auditive and visual stimuli reduces saccadic latency -19-. References 1. Rayner, K., & Fisher, D. L. Letter processing during eye fixations in visual search. Perception & Psychophysics. 1987; 42: 87- 100. 2. Findlay, J. M. Saccade target selection during visual search. Vision Research. 1997; 37: 617-631. 3. Hooge, I. T., & Erkelens, C. J. Peripheral vision and oculomotor control during visual search. Vision Research. 1999; 39: 1567- 1575. 4. Fischer B, Biscaldi M, Gezeck S. On the development of voluntary and reflexive components in saccade generation. Brain Research, 1997; 754:285-297. 5. Brockmole, J. R., Carlson, L. A., & Irwin, D. E. Inhibition of attended processing during saccadic eye movements. Perception & Psychophysics. 2002; 64, 867-881. 6. Rayner, K. Eye movements in reading and information processing: 20 years of research.Psychological Bulletin, 1998; 124: 372- 422. 7. Sooha Park Lee, Jeremy B. Badler, Norman I. Badler. Eyes alive. SIGGRAPH 2002: 637-644. 8. Martinez-Conde, S., Macknik, S.L., Hubel, D.H. The role of fixational eye movements in visual perception. Nature reviews Neuroscience, 2004 (5):229-240. 9. John M. Findlay, Valerie Brown, Iain D. Gilchrist. Saccade target selection in visual search: the effect of information from the previous fixation. Vision Research, 2001; 41: 87–95. 10. Schachar Ronald A.; Bax Andrew J. Mechanism of Human Accommodation as Analyzed by Nonlinear Finite Element Analysis. Compr Ther. 2001 Summer; 27(2):122-32. 11. Beers AP, van der Heijde GL. Analysis of accommodation function with ultrasonography. Documenta Ophthalmologica. 1996-97; 92(1):1-10. 12. Moses RA. Acomodación. In: Fisiología del ojo de Adler. 8th ed. Buenos Aires: Panamericana, 1988:285-302. 13. Morris A, Temme LA. The time required for U.S. Navy fighter pilots to shift gaze and identify near and far targets. Aviat Space Environ Med. 1989 Nov; 60(11):1085-9. 14. Horwitz GD, and Newsome WT. Separate signals for target selection and movement specification in the superior colliculus. Science. 1999; 284: 1158-1161. 15. Dorris MC, and Munoz DP. Saccadic probability influences motor preparation signals and time to saccadic initiation. J Neuroscience. 1998; 18: 7015-7026. 16. Becker, W. & Jurgens, R. An analysis of the saccadic system by means of double step stimuli. Vision Res. 1979; 19(9):967-83. 17. Caspi A, Beutter BR, Eckstein MP. The time course of visual information accrual guiding eye movement decisions. Proc Natl Acad Sci U S A. 2004 Aug 31; 101(35):13086-90. 18. Blohm G, Missal M, Lefevre P. Processing of retinal and extraretinal signals for memory-guided saccades during smooth pursuit. J Neurophysiol. 2005 Mar; 93(3):1510-22. 19. Colonius H, and Arndt P. A two-stage model for visual-auditory interaction in saccadic latencies. Percept Psychophys. 2001; 63: 126-147. Competing interests: None declared
Visual sequence in a game of offside in football. 4 April 2007
FRANCISCO BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Visual sequence in a game of offside in football.	Five objects1 take part in an offside game: the ball, two attacking players and the last two players of the defending team. Although more players can take part in some cases. The offside rule requires that the human eye detects the exact geographical location of all the players that take part in a game, "in the precise moment when the ball is being passed2". The fixational point of the Referee and the Assistant Referee (AR) should always be the player who is touching the ball, in order to know the precise moment when the ball is passed. This physiological situation requires that in the precise moment when the ball is being passed, the eye should carry out at least three saccades3,4: the first one to locate the player who receives the ball, the second one to locate the second last defender and the third movement to locate the last defender (because sometimes the goalkeeper has left the goal and he is not the last defender). After each saccade an eye ocular fixation5 is necessary to acquire and to integrate all the visual information of the player the Referee is interested in. All that information must be processed5,6,7 in the human brain and moreover to decide what players participate actively in a game of offside8,9. The visual sequence is the following (Fig.1). The player who is playing the ball, and who is moving, is spotted thanks to smooth pursuit eye movements10. In a probable offside game, in the moment when the ball is passed, the Referee and the AR carry out a first fixation movement11 (which lasts 30msec). Then, they get all the information, which is processed in the brain and at the same time the Oculomotor System prepares to carry out several consecutive saccades12, to detect the exact geographical position of all the players who take part in that game in the football pitch. After the first fixation movement, the first saccade3,13,14 is carried out (duration: 80msec of latency + 30 msec of duration) which finishes with the second fixation. The second fixation (duration 30msec) is carried out to process the exact geographical location of the player who is going to receive the ball. After the second fixation, the second saccade starts (duration 30msec) which finishes with the third fixation of the second last defender (duration 30msec), to obtain visual information to know his relative position compared to the player of the opposing team who received the ball and to detect if there is an offside or not. If the goalkeeper is not the last defender, it is precise to carry out a third saccade (duration 30msec) and a fourth fixation (30msec) in order to locate the last player of the opposing team. All this process is 230msec long up to the third fixation and 290 msec long up to the fourth fixation (Fig.1. Game A: Offside position. Game B: There is no offside position. The visual sequence is the same in both games). In order to carry out this saccadic sequence, all the players must be within the visual field. If any of the players is not within it, it would be necessary to move the head to locate the players. And that would mean that the amount of time to detect the players would obviously be higher. To have a wider visual and graphical knowledge about saccades, fixations and smooth pursuit eye movements, it is advisable to read the web page from the University of Western Ontario15, Canada. REFERENCES 1. 1. Belda Maruenda, F. Can the human eye detect an offside position during a football match? British Medical Journal. 2004, December 18; 329 (7480): 1470 -1472. 2. 2. International Football Association Board. New Laws of the game. Zurich: Fédération Internationale de Football Association (FIFA), 2006. http://www.fifa.com/en/regulations/regulation/0,1584,3,00.html 3. 3. Fischer B, Biscaldi M, Gezeck S. On the development of voluntary and reflexive components in saccade generation. Brain Research, 1997; 754:285-297. 4. 4. Brockmole, J. R., Carlson, L. A., & Irwin, D. E. Inhibition of attended processing during saccadic eye movements. Perception & Psychophysics. 2002; 64, 867-881. 5. 5. Martinez-Conde, S., Macknik, S.L., Hubel, D.H. The role of fixational eye movements in visual perception. Nature reviews Neuroscience, 2004 (5):229-240. 6. 6. John M. Findlay, Valerie Brown, Iain D. Gilchrist. Saccade target selection in visual search: the effect of information from the previous fixation. Vision Research, 2001; 41: 87–95. 7. 7. Becker, W. & Jurgens, R. An analysis of the saccadic system by means of double step stimuli. Vision Res. 1979; 19(9):967-83. 8. 8. Blohm G, Missal M, Lefevre P. Processing of retinal and extraretinal signals for memory-guided saccades during smooth pursuit. J Neurophysiol. 2005 Mar; 93(3):1510-22. 9. 9. Colonius H, and Arndt P. A two-stage model for visual-auditory interaction in saccadic latencies. Percept Psychophys. 2001; 63: 126-147. 10. 10. Blohm G, Missal M, Lefevre P. Direct evidence for a position input to the smooth pursuit system. J Neurophysiol (February 23, 2005). doi:10.1152/jn.00093.2005. 11. 11. John M. Findlay, Valerie Brown, Iain D. Gilchrist. Saccade target selection in visual search: the effect of information from the previous fixation. Vision Research, 2001; 41: 87–95. 12. 12. Caspi A, Beutter BR, Eckstein MP. The time course of visual information accrual guiding eye movement decisions. Proc Natl Acad Sci U S A. 2004 Aug 31; 101(35):13086-90. 13. 13. Rayner, K. Eye movements in reading and information processing: 20 years of research. Psychological Bulletin, 1998; 124: 372- 422. 14. 14. Sooha Park Lee, Jeremy B. Badler, Norman I. Badler. Eyes alive. SIGGRAPH 2002: 637-644. 15. 15. The University of Western Ontario. 2003. http://www.physpharm.fmd.uwo.ca/undergrad/sensesweb/L11EyeMovements/L11EyeMovements.swf Competing interests: None declared
Which probabilities have referees and Assistant Referees of detecting an offside? 7 May 2007
Francisco BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Which probabilities have referees and Assistant Referees of detecting an offside?	Reckoning the probabilities that Referees and AR's have of "getting right" an offside can be quite a difficult job, because they depend on a series of too wide and maybe infinite variables. From these variables, we can underline: the attention on the game, the floodlighting, the luminosity or the colour of the players' t-shirts, the stripes on the grass, how the Refere and the AR1 are located during the game, the insertion of other players in the game... However, in the last analysis, and despite all the variables, a player can be in an offside position or not. For the referee it is "heads or tails" and, as he is not capable of spotting it, he has to make a decision with just two possibilities. That means that Referees and AR's always have 50% of probabilities to "get an offside right", but also 50% of errors.          It is possible to get the minimum distance which separes both players (the first player and the second last defender) so that the Referee and the AR's can detect an offside position with no visual error. This distance is calculated in Table 1 for 230msec, the time that the eye needs to detect the two main players, taking into account their speed, if they start from static positions (start of the race speeding up) or if they are already running, and if they stand up statically (they do not move).   Z 1.   X: ► A       Y: ◄ A 2.   X: ► A       Y: ◄ C 3.   X: ► C       Y: ◄ A 4.  X: ► C      Y: ◄ C Space >174.92cm >277.54cm >277.54cm >380.16cm Z 5.   X:  ► A       Y:       E  6.   X:  ► C        Y:       E   7.   X: ◄ A       Y:      E 8.  X: ◄ C      Y:      E Space >87.46cm >190.08cm >87.46cm >190.08cm X: Forward player       Y: Defender     A: Acceleration: the player is speeding up.      C: Race: The player is in the middle of the race. Z: Relative positions of the players from both teams.   ► Direction: To the opposite goal. ◄ Direction: To the middle of the pitch. E: The player is in a static position, whith no movement. 7 y 8: The forward player, in an offside position, runs back to the middle of the           pitch, to avoid the Referee and the AR watching the offside.            Table 1. Minimum distance which separes both players to be able to see and judge               an offside position avoiding visual errors.   As we can see in Table 1, the minimum distance that separates these two players to detect an offside has to be bigger than 87.46cm (position 5). In this position the forward player runs to the opposite goal, speeding up from a static position and the second last defender is static, with no movement.        REFERENCES     1.  Oudejans RR, Verheijen R, Bakker FC, Gerrits JC, Steinbruckner M, Beek PJ. Errors in judging 'offside' in football. Nature. 2000 Mar 2;404(6773):33. Competing interests: None declared
Physical laws and Offside Rule 9 May 2007
Francisco BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Physical laws and Offside Rule	Which distance in centimeters can a football player run in 200 milliseconds? The problem arises when we apply Physical laws to the Offside and to the Occular Neurophysiology: speed, space, time and acceleration are incompatible with this rule application.                 In order to obtain these data, I have used the results of the final race of the 100 metres flat race of the 1997 World Championship in Track and Field, which took place in Athens1, Greece. I compare the average results of the eight finalist athletes with the results of a football player who would have run 100 metres in 13 seconds, quite a slow speed for a professional player (Table 1). The distance ran by the football player in the  first 10 metres is the addition of the reaction time plus the time needed to run those 10 metres. From the results in Table 1 we can deduce that while the eyes of the Referee and of the Assistant Referee (AR) need 230msec2 to detect the player who the ball was passed and the second last defender, both of them may have changed their position in the field from the moment when the ball was passed. This distance will be of 76.05cm in 200msec if they started from a static position, depending on how the players speed up, or of 165.29cm if the players were already running. These data have an added value if we take into account that, generally, the forward player runs to the opposite field, and the defender to the center of the pitch, to try to play an offside position on the forward player. In position A, Fig.1 (Relative change in the players' locations in an offside position), we see a player who is not in an offside position exactly in the moment when the ball is passed from one of his team mate, because he is 1 metre away from the second last defender. However, if both players run in opposite directions, 200msec later, in position B the forward player is located 52cm before the defender (they start the race from a static position); and in position C he is located 2.30m before the defender (both of them are running). In situation B and C the player starts from a correct position, but, 30msec later, when the Referee or the AR would finish the saccadic sequence, they would say that there is an offside, when it is not true. Fig. 1. Relative change in the players' locations in an offside position. AR´s try to solve the problems of this rule appliance with two mistaken techniques. 1. Some AR´s try to run next to the first player who is playing the ball. However the AR has to carry out saccades continuously to detect the moment when the ball is passed and the geographical location of the fastest player. In the precise moment when the ball is being passed, the AR has to look again to that player, but during the period of the sequence fixation-saccade-fixation the player has the opportunity to change his position in the pitch. 2. The rest of the AR´s are just looking at the first player and they try to listen to the sound of the kick to the ball in the moment when the ball is going to be passed. But this means an additional problem, because the speed of sound is slower than the speed of light and during that time difference (during the time that takes the ear in perceiving the sound of the ball), the first player may have changed his position. REFERENCES 1. Brüggemann, GP, Koszewski D, and Müller H (Editors). Biomechanical Research Project Athens 1997. Final Report. Oxford, UK: MMSU, 1999. 2. Belda Maruenda, Francisco. Visual sequence in a game of offside in football. http://www.bmj.com/cgi/eletters/329/7480/1470 Competing interests: None declared
Which criteria should the technological media follow to detect an offside? 25 May 2007
Francisco BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Which criteria should the technological media follow to detect an offside?	As it happens with the human eye, the technological media are subjected to the tyranny of the offside rule, because they have to detect all the players who take part in this game "in the precise moment when the ball is being passed". That is why physics play such an important role evaluating the media. The most important premise is time and any technological media cannot consume time to detect the players, because they can move within the pitch and they wouldn't be in the initial position (when the ball was passed). So a media which does not consume time should be used. Nowadays there is not such media, because the electrical, electronical, radiofrequency or laser signal transmission needs time. Will there appear a non time consuming media in the future?          Currently there is just a way to know if a player was or not in an offside position, without any visual error. We can only affirm that there was an offside or not repeating and freezing the image on television, in the precise moment when the ball is being passed. In that case, it would be necessary to stop the match to confirm the offside, time which could be used for advertisements. Competing interests: None declared
IS IT POSSIBLE TO SPOT AND JUDGE AN OFFSIDE POSITION DURING A FOOTBALL MATCH? 28 May 2007
Francisco BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: IS IT POSSIBLE TO SPOT AND JUDGE AN OFFSIDE POSITION DURING A FOOTBALL MATCH?	The key factor in this rule application is that the player must be in the offside position exactly in the moment when the ball is passed from one of his team mates, not when he receives the ball or when the ball is en route between the players1. In order to achieve this axiom, it is necessary to stop time2 and to locate all the players who take part in that game in zero milliseconds. If some time passes, although it is just 1msec, the players can change their position in the pitch.          In an offside, the Referee and the Assistant Referee may have within their visual field five objects3: two attacking players, the last two players of the defending team and the ball. The Referee and the AR's need time to detect an offside position, and this time is mainly defined by the saccades (latency and duration) and the eye fixations4,5. This is incompatible with the philosophy of football and with physics, because the players have speed and acceleration to change their position within the pitch in a specific amount of time, so that they cannot be located in the original position, exactly when the ball was passed5.          When an offside is misjudged, human mistakes are always mentioned. However, that is not correct. To make a mistake means to carry out incorrectly an action that we are qualified to do, and that we can carry out correctly. The Referee and the AR's are physiologically incapable of detecting an offside4,5. That is why they can just "get right" some of the offsides, because they have 50% of possibilities of judging correctly an offside6.       The Referee, the Assistant Referees, the public at the stadium and the viewers at home have to perform saccadic movements and fixations2,4,5.      A Referee and an AR may find three different physiological situations in an offside game:      1. If all the players who take part in an offside are not within their visual field, they would never know if there is or not an offside.      2. When all the players are located within the visual field, at least 230msec are needed to locate the two main players in that game (the player who the ball was passed and the second last defender).      3.  If there are players who are located more than 6 metres away or more than 6 metres closer to the Referee or the AR, the eye needs to accommodate7, and this physiological situation needs more than 1 second.          Which is the problem of the offside rule that makes it impossible for the human eye and technological media8 to detect it? The problem is a notion error, because when it was created, nobody took into account the time needed to locate the different players who take part in the game. That time is fantastically used by the players to change their position in the pitch, so that they cannot be detected exactly in the precise moment when the ball is being passed.         The offside rule in football was introduced9 in 1866 (19th century). Since then, such a simple concept has gone unnoticed. Sometimes, the mankind has needed centuries to understand very simple concepts and to accept them. We are living in the 21st century, the century of technology and it is impossible to detect and judge an offside, not even using technological media.   REFERENCES   1.  Belda Maruenda, Francisco. 1 July 2006: Offside rule in football was modified substantially. http://www.bmj.com/cgi/eletters/329/7480/1470#162676 2.  Belda Maruenda, Francisco. Physical laws and Offside Rule. http://www.bmj.com/cgi/eletters/329/7480/1470#165009 3.  Belda Maruenda, Francisco. Can the human eye detect an offside position during a football match? British Medical Journal. 2004, December 18; 329 (7480): 1470 -1472. 4.  Belda Maruenda, Francisco. Physical Laws, Ocular Neurophysiology and offside rule. http://www.bmj.com/cgi/eletters/329/7480/1470#162680 5.  Belda Maruenda, Francisco. Visual sequence in a game of offside in football. http://www.bmj.com/cgi/eletters/329/7480/1470#162974 6.  Belda Maruenda, Francisco. Which probabilities have referees and Assistant Referees of detecting an offside? http://www.bmj.com/cgi/eletters/329/7480/1470#165007 7.  Caspi A, Beutter BR, Eckstein MP. The time course of visual information accrual guiding eye movement decisions. Proc Natl Acad Sci U S A. 2004 Aug 31; 101(35):13086-90. 8.  Belda Maruenda, Francisco. Which criteria should the technological media follow to detect an offside? http://www.bmj.com/cgi/eletters/329/7480/1470#166690 9.  Olivós Arroyo R. Teoría del fútbol. Seville: Wanceulen, 1992.   Competing interests: None declared
Conclusions: Offside Rule versus Ocular Neurophysiology and Physical Laws 1 June 2007
Francisco BELDA MARUENDA, Specialist in Family Medicine Centro de Salud de Alquerías, C/ Ramón Fernández Miñarro, 30580, Alquerías, Murcia, Spain. Send response to journal: Re: Conclusions: Offside Rule versus Ocular Neurophysiology and Physical Laws	1.     Nowadays, in real time, nobody can spot and judge an offside, not even using technological media1. 2.     The keypoint of the offside in football is to do it "in the precise moment when the ball is played2,3". 3.     In that moment, the Referee and the Assistant Referees eye should have within their visual field five objects4: the ball, two players of the attacking team and two players of the defending team. 4.     The human eye needs to perform saccadic and fixational movements in order to detect those players5,7. Time is necessary to do that, but players make profit and change their position meanwhile6. 5.     The offside is also incompatible with physical laws related to speed, space, time and acceleration5,6,7. 6.     Conceptually, the offside requires stopping time6 to be applied correctly. But this is something impossible, even with technical media1. 7.     A Referee does not make an error when he misjudges an offside: He is physiologically unable to judge it5,7,8.        REFERENCES   1.      Belda Maruenda, Francisco. Is  it  possible  to  spot and judge an offside  position  during a football match? http://www.bmj.com/cgi/eletters/329/7480/1470#166854 2.      International  Football  Association  Board.  New  Laws  of   the   game.   Zurich: Fédération Internationale de Football Association (FIFA), 2006. http://www.fifa.com/en/regulations/regulation/0,1584,3,00.html 3.      Belda Maruenda, Francisco. 1 July 2006: Offside rule  in  football  was  modified substantially. http://www.bmj.com/cgi/eletters/329/7480/1470#162676 4.      Belda Maruenda, Francisco.  Can   the   human   eye   detect  an  offside  position  during  a  football   match?  British  Medical  Journal.  2004,  December  18; 329 (7480): 1470 -1472. 5.      Belda Maruenda, Francisco. Physical Laws, Ocular Neurophysiology and offside rule.  http://www.bmj.com/cgi/eletters/329/7480/1470#162680 6.      Belda Maruenda, Francisco.  Physical  laws  and  Offside  Rule. http://www.bmj.com/cgi/eletters/329/7480/1470#165009 7.      Belda Maruenda, Francisco. Visual  sequence  in  a  game  of  offside in football. http://www.bmj.com/cgi/eletters/329/7480/1470#162974 8.      Belda Maruenda, Francisco.  Which  probabilities  have  referees  and  Assistant Referees of detecting an offside? http://www.bmj.com/cgi/eletters/329/7480/1470#165007 Competing interests: None declared