But Seriously, Mcenroe May Have Been Right

John McEnroe is renowned for his bad-tempered Center Court tussles with umpires over whether his opponent's ball was on the line or out, which cost him thousands of dollars in penalties. Now a study of line calls by tennis officials suggests he may have been right all along.

An analysis of challenges by players in 15 professional tennis tournaments in 2006 and 2007 has found that line judges are wrong nearly 40% of the times when they are challenged. More than half of these challenges occur when the ball is less than 2.25cm from the line, so McEnroe's shouts of "You cannot be serious!" were probably unfair.

Dr George Mather at the University of Sussex's psychology department, studied data on 1,473 challenges by 246 professional players. When a challenge is made in an Association of Tennis Professionals tournament, the officials record who made the call, where the Hawkeye technology placed the ball and whether the challenge was upheld or rejected. The system uses cameras to follow the movement of the ball in 3D.

Mather found that 95% of challenges refer to balls that bounce within 10cm of the line, although in one case a player challenged a call when the ball was 45cm from the line. In that case the line judge had got it right, but overall, when they are challenged, they are wrong 39.3% of the time.

When Mather extrapolated this figure to all the calls where the ball is within 10cm of the line (many of which go unchallenged), he estimated that line judges are wrong about 8% of the time. The study is reported in the Proceedings of the Royal Society of London.