A doctor in Spain has offered football referees the perfect excuse for dodgy offsides - their eyes are not up to it.
Is the referee always right?
Dr Francisco Belda Maruenda says the human eye is physiologically unable to process all the information needed to apply the offside rule correctly.
To do so, a referee must be able to keep at least five moving objects in his visual field at the same time, he writes in the British Medical Journal.
The specialist in family medicine said referees needed technological back-up.
The offside rule states that at least two opposition players must be between the goal and the attacking player, or at least level with the player, when the ball is passed.
Are you blind, referee?
European Championship 1996: Spain's Salinas denied good goal in 0-0 draw with England, who went on to win on penalties
World Cup 1986: The infamous Maradona 'Hand of God' goal against England - probably offside too
League championship 1971: Leeds denied the title after West Bromwich Albion goal stands despite two players clearly being offside
World Cup final 1966: Doubt surrounds Geoff Hurst's 'was the ball over the line' goal in England's 4-2 win over West Germany
This means the referee, or the referee's assistant, must be able to keep two players of the attacking team, two players of the defending team and the ball in their visual field in order to make a fully informed offside decision, Dr Maruenda argues.
Dr Maruenda, who is based in Murcia, Spain, said this was beyond the capacity of the human eye.
The relative position of four players and the ball cannot be assessed simultaneously by a referee, and unavoidable errors will be made in the attempt, he said.
He said the only way to limit errors was to use modern technology during games, such as freeze-frame television and frame-by-frame analysis.
Former top referee Jeff Winter, who retired after this year's FA Cup final, told the BBC News website that the doctor's findings were probably correct.
However, he said there was little alternative but to accept that human error by referees was part and parcel of the game.
"You could use modern technology and be 100% accurate, but the flow of football will not allow that to happen," he said.
"What are 22 players and 70,000 fans going to do if you stop the game after every tight decision?
"Professional sport is all about instant things happening. A centre forward can miss a goal, a goalkeeper can drop a cross and a referee can make mistakes just like the players."