Chainkeen|US Open tennis balls serving up controversy, and perhaps, players' injuries

NEW YORK — A tennis ball seems simple enough. It’s a pressurized piece of rubber covered with neon yellow felt. How different could Chainkeenone be from another? 

The answer — especially at the top level of tennis — is quite a bit. The brand of ball, the weave of the felt, the way they bounce and how they react after getting hit a bunch of times are all variables that have an impact on how matches are played. 

And at this US Open, at least one player is blaming them for an injury.

After beating American Peyton Stearns on Monday in the round of 16, Wimbledon champion Marketa Vondrousova pulled out of the doubles competition citing arm pain that she attributed to the heaviness of the Wilson brand balls being used this year. Vondrousova hasn’t pulled out of the singles competition and expects to play her quarterfinal against Madison Keys on Wednesday. 

“They are very heavy and the season is long, so I feel like, you know, you just have to fight through it,” she said.

Under International Tennis Federation rules, there are actually small variables in the specifications allowed for tournament balls: About 1/10th of an inch in diameter and about three grams of weight. Balls are also branded as “regular duty” or “extra duty” which describes the thickness of the felt weave. 

For commercial sales and recreational use, extra duty is generally advertised as suitable for hard courts because they are more durable and last longer while regular duty is better for a softer clay court. 

Every tournament in pro tennis chooses which balls to use, generally as part of a sponsorship deal. The Australian Open uses Dunlop balls, the French Open uses a specialty ball from Wilson designed for their specific red clay and Wimbledon uses a Slazenger ball.

But last year, some players on the women's side — led by No. 1 Iga Swiatek — began to publicly wonder why they were playing regular duty balls at the US Open while the men played extra duty. Beyond the general theme of equality, Swiatek felt that the regular duty balls were light and difficult to control. Despite her complaints, she ended up winning the tournament.

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Tournament director Stacey Allaster said the decision on which ball to use falls with the WTA, but that it has to be made a year in advance to give Wilson enough time to manufacture the volume of balls required for the event.

So the decision was made: The women would play with the same balls as the men. 

“This is a trial,” Allaster said. “We'll expect the WTA to tell us at the end of the 2023 US Open if they'd like to continue with the Wilson Extra Duty or they prefer to go back to the regular felt balls. It’s 100% the athletes' decision. We're happy to do whatever the athletes want as it relates to the ball. So is our long time, 45-year partner Wilson.”

This year, though, complaints about the balls are popping up for both the men and women. 

Vasek Pospisil, who has been highly involved in tour politics as a former ATP players' council member and co-founder of the independent PTPA players organization, posted on the social media site X (formerly Twitter) that “The balls have been getting incrementally heavier and surprise surprise, it's killing our bodies. Almost every player I've spoken to feels the same way. I've never seen more wrist, elbow and shoulder injuries in the locker room.”

The theory, as Pospisil framed it, is that tours want a slower, heavier ball to promote longer points. But the reality is that ball controversies and complaints have been happening for years. Players have become used to adapting to different kinds of balls as they go from tournament to tournament, but WTA players' council member Jessica Pegula said there would ideally be some consistency based on surface.

"The ball issue is so elaborate," she said. "Like last year we learned that sometimes they can come from different manufacturers, sometimes they're made differently. In Cincinnati they didn't use a typical hard court, they used a different surface, which was like skinning the balls to going really, really small. In Montreal, they're all extra duty and were fluffing up like this (gestures the size of a cantaloupe) in two minutes. There's so many elements.

"They play different based on the conditions, the court surface, where they're coming in, what country you're in, who's playing with them. It literally is all over the place."

The heaviness of the balls here, though, has been a common theme and seems to have some validity as an issue players are thinking and talking about.

Caroline Wozniacki said that it “sticks to your racquet a little bit more” and thus it would favor the players with more power.

“I think it’s easier for them to hit through that ball,” she said. 

And there does seem to be some evidence that power-reliant players are having success here. On the men's side, quarterfinalists tilt heavily toward explosive power in the likes of Andrey Rublev, Ben Shelton, Taylor Fritz and Carlos Alcaraz. Same thing on the women’s side with Jelena Ostapenko and Madison Keys — two of the heaviest hitters on the WTA tour — matching their best Grand Slam runs of the year. 

But is a heavier ball contributing to soft tissue problems in the wrists, elbows and shoulders that have to absorb the weight of it?

“Some women have issues with their arm playing with the heavier ball in the mixed doubles so it will be interesting to see how it works out now that everyone is using it in all competitions,” former champion Martina Navratilova said in an interview before the tournament with UK-based Sky Sports.

Based on what Vondrousova said Monday, her warning might have been on target. According to Pegula, player conversations about what ball to use for the women in 2024 are happening right now.

"Obviously the players' health is the most important," Pegula said. "I joke with the council because I feel like I don't like any of the balls, so I just kind of took myself out of it. But yeah, it's something we're going to have to look at."