September 6, 2008, 8:18 pm
Hawk-Eye Wins Over Players, Fans and Officials
By Aron Pilhofer
In a small booth overlooking Arthur Ashe Stadium, a team of technicians sits hunkered amid a tangle of wires, monitors and whirring computers. Though they are more than 10 stories above the match going on below, in a sense this is the best seat in the house.
The network of cameras and computers they control can track the flight of a tennis ball with an accuracy measured in millimeters — 3.6 to be exact. Overseeing it all is Paul Hawkins, the thin, sandy-haired, 30-something Englishman who had the crazy idea a few years ago to do for tennis what no other professional sport seems to have managed: create an instant replay system that works.
“I have a technology background. I love sports,” explains Hawkins, who holds a doctorate in artificial intelligence. “So, I kind of had an opportunity to combine my two passions.”
The result was Hawk-Eye, arguably the most successful instant replay system in sports. Since its introduction at the Open three years ago, Hawk-Eye has won over fans, players and even officials.
“And it’s not often you can say something like that,” said Chris Widmaier, senior director of public relations for the United States Tennis Association. “It has been fantastic for the game."
In fact, about the only criticism of Hawk-Eye is that it isn’t used more widely. Currently, instant replay is only available on the two larger show courts: Ashe and Louis Armstrong Stadium. This was an issue twice for top-ten player Andy Murray, whose second- and third-round matches were marred by numerous questionable line calls and umpire overrules.
“I’d rather have Hawk-Eye on every single court, but I understand it’s very, very expensive,” Murray said.
In addition to the five-figure cost of the system each year, the infrastructure improvements — such as a video-enabled scoreboard — make it cost-prohibitive to put the system on all 14 Open courts.
But Hawk-Eye has been so well received, the U.S.T.A. is seriously considering investing $100,000 to add the system to a third court — the Grandstand — next year, according to David Brewer, tournament manager for the U.S. Open.
The system isn’t the first electronic line calling system the Open has tried. Fans probably remember (perhaps fondly, perhaps not) Cyclops, which was in use throughout professional tennis for nearly two decades. The system was far from perfect: It was limited to the service line, prone to error, and because it relied on beams of infrared light, Cyclops could be triggered by insects or other stray objects.
U.S.T.A. officials had been testing alternative electronic line calling systems for years, but every system they looked at until Hawk-Eye was deficient in some critical way, said Rich Kaufman, the U.S.T.A.’s director of officials and chief umpire for the U.S. Open.
“Even Hawk-Eye, when we first looked at it six or seven years ago, wasn’t accurate enough, but it is now,” he said.
The big breakthrough, Hawkins said, was not relying on optical devices to determine where a given shot lands — a surprisingly difficult thing to measure accurately. Hawk-Eye does utilize a system of 10 cameras to track the speed and trajectory of a ball in flight, but that’s only part of the magic. The rest is done exclusively through computer modeling.
Because no tennis court is exactly flat and no line precisely straight, before the tournament Hawkins’s team takes thousands of precise measurements of the dimensions and contours of each court, which are then converted into a three-dimensional computer model. Hawk-Eye’s virtual world takes into account other real-world factors that can affect accuracy, like the amount a ball compresses when it hits the court and even the temperature of the court itself.
“During warm days, the court actually changes size as it heats up or cools down,” Hawkins explains.
When the ball flight data is fed into the computer model, the result is a system that is so precise it’s difficult to measure.
“The published stuff says 3.6 millimeters, but our system is actually more accurate than that,” Hawkins said. “It does become a bit of a law of diminishing returns because there’s error in the measuring device we’re being measured against. Even if we got it down to zero millimeters, our testing results would never say that.”
Accuracy alone doesn’t explain why instant replay works for tennis where it hasn’t for other professional sports, Kaufman said.
“We didn’t want long delays like in American football, where you have to go through three ads before you get a decision,” he said. “The good thing about Hawk-Eye is the results are immediate.”
But perhaps the biggest key to its acceptance among officials is that it matches an existing appeal process already in the rules, Kaufman said. On clay, the ball leaves clear marks where it strikes the court and the umpire is allowed to use that mark to overrule incorrect calls. Hawk-Eye brings that same procedure to the other two surfaces: grass and hard courts.
“The players understand clay court procedures. The umpires understand clay court procedures, and because of that I think there has been a very easy adjustment for everyone,” he said.
Kaufman doesn’t pretend Hawk-Eye is universally beloved by linesmen and umpires. “Most were probably a little tentative when it was first around, but we have gotten used to it,” he said.
One big positive for officials has been to show that they are right the vast majority of the time, Kaufman said. Only about 30 percent of instant replay appeals result in overruling of the original call.
“Before this, if people saw a player arguing they assumed the player was right,” he said. “The good thing about Hawk-Eye is it shows that officials are a lot more correct than people ever give us credit for.”
And that’s precisely what Hawkins wants.
“A good umpire doesn’t get noticed. In a sense, we don’t want to be in the limelight,” he said. “A kind of testament to how well we do is how long we’re around, and how few headlines we create."