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A look at Hawk-Eye electronic line calling technology in tennis

In tennis, the outcome of a game, set, match and even championship can turn on a couple of millimetres. Even the best line judges and umpires in the world can sometimes get it wrong, but up until relatively recently, players had no comeback if they considered themselves hard done by. Hawk-Eye has changed all that, with the concept of the player challenge now a familiar one at top-level tournaments.

So what exactly is Hawk-Eye? Is it always a good thing? What does it tell us about the possible future of tennis? We take a look.

The bad old days: why Hawk-Eye (or something like it) was inevitable

“You cannot be serious! That ball was on the line! Chalk flew up!”

John McEnroe’s frustrated outbursts were a staple of the early eighties. But some of the time at least, he may have had a valid point. In 2008, researchers at the University of California looked in detail at the way the human brain keeps track of moving objects. The results suggested that our struggle to keep track of high speed objects in motion leads us to mentally reposition an object where we think it should be.

The big problem for tennis players is that there’s often a tendency to overcompensate; a bias that leads us to think that the object is further along its path than it really is. This suggests that when a point is pretty close, an umpire is significantly more likely to make a mistake by calling a ball out than calling it in. Sure enough, when the team looked at 83 incorrect calls from a random selection of 4,000 tennis points from the previous season, it was shown that 84% of them were wrong ‘out’ calls.

Even without the science, it had long been clear that something needed to be done about the small but nonetheless significant element of human error inherent in the old way of doing things. Umpires got it right most of the time; but with so much at stake, and in an era of 130 mph serves, this wasn’t quite good enough. The trick was to try to bring in a system that was fair but that didn’t ruin the flow of the game.

How does Hawk-Eye work?

Invented by a Brit, Dr. Paul Hawkins, Hawk-Eye made its professional debut in 2001 - originally as a televisual commentating aid in cricket. It was given the green light as an officiating aid by the International Tennis Federation (ITF) in 2005 and first appeared at Wimbledon in 2007.

The tech is based on the instant interpretation of data from multiple cameras mounted strategically around the court. Vision processing software enables the computer to read and combine this information in an instant, tracking the ball’s path and producing an accurate 3D representation of it. This can then be viewed by officials, players, spectators and, of course, television audiences - often via a big screen ‘jumbotron’.

In its early days, tournament organisers who used Hawk-Eye were free to decide how many challenges each player would have. By 2008, the four governing bodies had agreed on a uniform system of challenge rules: a maximum of three unsuccessful challenges per set, with one extra added if the set goes to tiebreak.

Is everyone a fan?

Over the years, Roger Federer has earned a reputation as the most high-profile Hawk-Eye sceptic in tennis. As The Guardian noted in 2009; “He hates it, and is the only player to regularly protest against its use in public”. At the time, he’d made more challenges than any other player on the men’s tour; but a very high proportion of those were unsuccessful. The suggestion was that he challenged so often because he considered it to be fallible and he thought there was a chance of being gifted a point.

By contrast, word from Hawk-Eye’s senior systems engineer is that current World Number One Novak Djokovic also happens to be the world’s best when it comes to dealing with the technology, with the highest proportion of successful challenges among top players. The majority of players now accept it as part and parcel of the game; the choice of whether and when to use a challenge adds an extra tactical dimension, while for spectators, the big screen replay adds to the drama - precisely because challenges have to be used sparingly.

Will Hawk-Eye replace line judges?

The providers of the technology confirm that in theory at least, it would be possible to remove the current system of officials’ calls from the adjudication process entirely, replacing it with Hawk-Eye. As John McEnroe has suggested, players could potentially be left to call their own lines, with the tech there as a back-up; meaning, “All of a sudden, things would get a whole lot edgier”.    

Already, some of the minor events on the tour rely solely on Hawk-Eye and many in the sport feel it’s only a matter of time before this becomes a matter of routine. The technology has already been a fixture in tennis for a decade; in a further decade’s time, perhaps the concept of the line judge in the sport’s most prestigious arenas will have been consigned to the past.

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