At the 2022 U.S. Open tennis tournament, which wraps up this weekend in Flushing Meadows, N.Y., technology has won: game, set, match.

Human line judges at the tournament have been entirely replaced by optical technology to determine whether balls are ruled in or out. Immediately after impact, a recorded voice shouts out the call: "FAULT!" for a wayward serve; "OUT!" for a ball that lands long or wide in a rally.

Gone are player challenges to questionable calls. No more furious players spewing venom at umpires for a ruling that went against them.

By replacing human line judges with the optical system called Hawk-Eye Live, "we're providing the players a fairer playing field with a lot more integrity, a much higher accuracy call," says Sean Cary, who oversees officiating for the United States Tennis Association (USTA), which runs the U.S. Open.

In the past, Cary says, when a player challenged a line judge's call and it was reviewed through the Hawk-Eye tracking system, the human turned out to be correct about 75% of the time.

Now, Cary tells NPR, "the automated line calling system is right pretty much 100% of the time."

Put another way: "We are millimeter accurate in terms of our line calling," says Benjamin Figueiredo, director of tennis at Hawk-Eye Innovations.

Some players say Hawk-Eye is not foolproof, and does occasionally make erroneous calls. But most seem to support the shift.

"It's pretty tough to argue with a computer. You always lose that battle," says professional tennis player Noah Rubin, who competed at the U.S. Open from 2013-2019 at the junior and men's levels and was the 2014 Wimbledon junior boys' champion. Automated line calling, he says, "takes away that anxiety of, 'I really hope the line judge or chair umpire doesn't mess this one up.' "

Hawk-Eye Live uses 12 cameras to track the path of the ball through space.

"No sensors. No lasers," says the company's Figueiredo. "It's all through optical tracking. ... The entire system is calibrated to the court. And the cameras essentially identify the X, Y, Z position at any given point."

When the ball lands out, he says, "we're automatically triggering the noises that you hear on court through the P.A. system... to call 'fault' or 'out' calls in the same way that you're used to a line judge doing that."

The U.S. Open's pivot to Hawk-Eye Live came in 2020, at the early peak of the COVID pandemic. To minimize the risk of infection spread, the tournament eliminated nearly all line judges, instead using Hawk-Eye Live on all but the two main courts. Tournament officials thought the system worked so well that now they use it exclusively.

With the switch to automation, about 250 line judges lost their jobs at the U.S. Open. But some of their voices live on: the recorded calls heard during play include the voices of line judges who went into a studio inside Arthur Ashe Stadium and, essentially, recorded their swan songs.

There are a variety of officials' voices in the database, male and female, calling plays with a range of dynamics and urgency.

"The thing that I think is really cool," says the USTA's Cary, "is that we've been able to program the system to know that if the ball is way out, it's going to be a softer out call. But if it's a really close one, like it would be with a live line umpire, they generally yell at the top of their voices to make sure everyone hears it."

Just like a baseball umpire, they're selling the call.

"Yes," agrees Cary. "Selling the call is a great way of explaining it."

Fewer people means a 'cleaner' court

Along with greater accuracy, Cary says there's another advantage to replacing line judges with automation. Now, with nine fewer people on the court, he says, "we're providing a much cleaner court for our broadcast partners and our sponsorship partners."

In other words, the TV networks and corporate sponsors are happier because the screen has less clutter – though Cary balks at that word: "I mean," he says, "clutter's not necessarily a nice word to call human beings."

The absence of line judges, however welcome, still strikes player Noah Rubin as visually odd.

"I'm usually not a tennis traditionalist," he says, "but there's something about having those line judges dressed up in the back of the court making the calls. There's definitely something missing there. It looks pretty empty on the courts."

But, he adds, "I think this is where sports have to get to. There's too much on the line to be decided by a missed call, by human error."

Other tournaments besides the U.S. Open have turned exclusively to Hawk-Eye Live instead of human line judges — including the Australian Open. There, the prerecorded voices making calls have included front-line workers who responded to both the COVID pandemic and wildfires, and the Aussie actress Rebel Wilson, who's a passionate tennis fan.

Last year, Hawk-Eye Innovation's Figueiredo caused a stir when he told the Sydney Morning Herald that his company had held discussions about replacing the "fault" and "out" calls with the names of sponsors shouted out instead.

"It's quite interesting," he said at the time. "You could have 'Ralph Lauren' being shouted out. That might wind a few people up after a while. It's certainly a possibility, yeah."

Asked about that prospect by NPR, Figueiredo responds cagily.

"Um ... there have been historical discussions that have been had," he says. "It's — um, it's not something that at the minute I guess anyone's particularly — well, has followed up on at the moment. ... It has previously been talked about. I guess I'd rather not go into details."

As for the U.S. Open, the USTA's Sean Cary predicts that automated line calling is here to stay: "Because we're providing a a fairer and more even contest to the players, with a higher level of integrity," he says, "it would be very difficult for us to move backwards now."