You cannot be serious? Line-judges are normally on the ball

TENNIS ace John McEnroe was wrong — tennis line-judges are remarkably sharp at pinpointing a ferocious forehand.

A review of challenges made in ATP (Association of Tennis Professionals) tournaments using data from Hawk-Eye, ‘the virtual umpire’, found officials were correct more often than players.

Only eight percent of “close calls” will be wrong in the average match, found Professor George Mather of Sussex University, Britain.

This confirms what the great tennis ‘bad boy’ John McEnroe could never accept — that officials do an excellent job.

Prof Mather, an expert in visual perception, was interested in how well humans are able to pinpoint objects moving at high speed. He wanted to see whether the limits observed under laboratory conditions were responsible for the errors made in tennis — errors the famous US tennis star was always so quick to highlight with his classic phrase: “You cannot be serious”.

“I wanted to see whether line-judges’ visual perception is as limited as McEnroe would have you believe. But officials are actually remarkably proficient,” said Prof Mather.

“Tennis balls can travel at 50 metres per second in a professional match, yet both line-judges and players can [pinpoint] ball bounce position with an accuracy of 30-40mm — a distance covered in less than a millisecond.”

Ever since the days of Romanian Ilie ‘Nasty’ Nastase, players have argued that bad line calls were ruining the outcomes of tennis matches and called for technology to resolve disputes.

In 2006, tournaments began using the Hawk-Eye ball tracking system, also used by cricket’s third umpire. The system’s software uses data from multiple cameras trained on the court to compute the position of the ball, to within 3mm.

Yet Hawk-Eye has been at the centre of several flashpoints, including last year’s Wimbledon final, where Roger Federer lost his temper after a Hawk-Eye decision.

There have been accusations of tour players using their allotted challenges purely to disturb their opponent’s rhythm — just as there were in the days of McEnroe and Nastase.

To investigate, Prof Mather studied data from 15 tournaments during 2006 and 2007.

He found that out of 1,473 challenges, the overwhelming majority (94%) were “close calls” — balls bouncing within 100mm of the line.

“When you watch tournaments, you often get the feeling players are indulging in gamesmanship. But from what I’ve seen, players only challenge when they genuinely believe there is an error,” said the Sussex researcher.

Although tour professionals varied widely in how many challenges they made — from seven challenges to 52 — the players who challenged most were correct just as often.

“It seems challenges genuinely reflect perceptual uncertainty, rather than gamesmanship,” said Prof Mather.