In or out? It’s one of the most important questions that’ll be asked during this year’s Wimbledon Championships and one that could be decided by the Hawk-eye electronic line judge.
But how exactly does it work? And how can players use it?
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Here’s everything you need to know…
How does Hawk-eye actually work?
Despite its name, this piece of umpiring sadly doesn’t rely on Wimbledon’s harris hawk/pigeon deterrent Rufus. The job instead goes to a network of 10 cameras spread around the court that capture 60 high-resolution images per second. At least five cameras cover every ball bounce.
A centralised computer system rapidly processes the images, triangulates the position of the ball and calculates a flight path (that’s the yellow streak you see behind the ball in the Hawk-eye graphics) with many mathematical calculations.
Hawk-eye collects data for every shot taken in the match, not just the close calls. This is to make sure all 10 cameras are doing their job – as well as providing plenty of talking points for analysts and pundits.
The 26-strong Hawk-eye team ensure the cameras are calibrated to the courtlines, and they have to do this when faded lines are repainted throughout the tournament.
During games, a team of four work from a commentary booth: two Hawk-Eye team members, one big-screen operator and one review official (a certified umpire).
How many times can players use Hawk-eye?
Here’s some good news for players: they’re given unlimited opportunity to challenge a call in each set at Wimbledon. However, there’s a catch: once three incorrect challenges are made, that player can’t challenge again until the next set.
If the set goes to a tiebreak, an extra challenge is awarded to each player.
It rarely happens, but the umpire can reject a challenge if it is an “unreasonable request or that it was not made in a timely manner”, according to the International Tennis Federation rules.
When was Hawk-eye introduced to Wimbledon?
After it was first tested in 2004, the system, invented by Paul Hawkins, was implemented on Centre and No.1 courts in 2007. The system is now used across Centre Court, and courts 1,2,3,12 and 18.
Players on courts without Hawk-eye have to solely rely on line umpires to make the right calls.
How accurate is it?
Not 100%. In fact, the Hawk-eye system has a 2.2mm margin of error, with some research claiming the system can be as much as 10mm off. Why? The ball may move too quickly to be properly captured on camera as all cameras have a finite frame-speed. As one University of Cardiff paper says, “if the frame-speed is, say, 100 frames per second, and the ball is moving at about 100 mph it will travel about 1.5 feet between frames”.
This margin of error can cause controversy during big points. For instance, in the 2007 Wimbledon final between Rafael Nadal and Roger Federer, a ball that appeared to be out was called in by 1mm.
There are other occasional problems with the system. During a 2017 match between Rafael Nadal and Borna Coric, the Hawk-eye graphic failed to show on screen, with Nadal appearing to be sceptical about the final call.
But despite the problems with Hawk-Eye, it’s a lot more reliable than human line judges. Studies have suggested 8.2% of all line calls involving balls within 100mm of a court line will be called incorrectly by line judges. This means you can expect line judges to make four errors per set.
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