You can't play tennis without tennis balls.

Yet an increasingly vocal group of players says that the tennis balls used on tour are behind a major problem: They're causing injuries. Top players contend the lack of consistency in the balls is linked to a rash of significant shoulder, elbow and wrist injuries.

As the season gets into full swing Sunday with the start of the Australian Open, players are ramping up pressure for changes.

"Right now if you go into the locker room, I want to say almost half the guys on tour ... are dealing with some kind of arm issue," said Vasek Pospisil, the co-founder of the Professional Tennis Players Association, a players advocacy group.

The world's No. 1 men's player, Novak Djokovic, who co-founded the players association with Pospisil, also says the tennis balls are a problem.

"There is certainly a connection between frequent injuries of the wrist, elbow and shoulder with ball changes," Djokovic told the sports website Sportal last year. "I am absolutely in favor of choosing one ball with which we will play all ATP tournaments."

After months of public outcry from players over the balls, their complaints finally appear to be having an impact.

The ATP and the WTA, the governing bodies for men's and women's professional tennis, respectively, last week announced a strategic review of the balls used on the tours, a move taken, they said, as "a direct result of player input."

In a joint statement, they said the goal is to deliver greater ball consistency, "while not adversely affecting revenue streams for tournaments."

In response to the announcement, Pospisil tweeted on X: "Really hope they are thorough with this and that's it's not just smoke and mirrors."

The balls keep changing

Pospisil, 33, said when he joined the tour 16 years ago, elbow injuries were rare, almost unheard of. He won the 2014 men's Wimbledon doubles title with partner Jack Sock, but he has suffered from elbow ligament and tendon tears that have derailed his career for the past two years.

The balls used during the grueling tennis season (which lasts about 11 months) often change from tournament to tournament, from week to week, depending on contracts that tournaments have with manufacturers.

With their finely calibrated strokes, players are attuned to slight variations in a ball's weight or pressure. And a lack of consistency isn't their only complaint. Chief among them is that the balls feel heavy upon impact.

"I have to hit the ball with significantly more force for the ball to even do anything, to try to make an effective shot," said Pospisil. "So right away you're applying a lot more force. There's more pressure on impact."

"Like a grapefruit"

Daniil Medvedev, the men's world No. 3, last year said the balls used in a tournament in Beijing quickly expanded and became fluffy, making aggressive, point-ending shots much more difficult. "They become like a grapefruit. ... We're basically playing 30-shot rallies because it's almost impossible to hit a winner."

The extended rallies increase fatigue and the pressure on a player's arm.

Taylor Fritz, the top American male player, posted on X about struggling with wrist problems due to frequent ball changes.

Robby Sikka, a physician with a focus on sports medicine who has consulted with the Professional Tennis Players Association, said, "There's no question that the changing of ball technology and the lack of consistency has had an impact on increasing injury risk to players."

He thinks tours should move quickly to determine whether certain balls may be unsafe. "We should pull those from the market just like the FDA does, or recall. ... We can't have the Wild, Wild West of tennis balls and expect this to be OK."

To Pospisil, there is a path to standardizing the balls without jeopardizing the revenue generated for tournaments from unique deals with manufacturers: a stricter standard ball, designed for specific surfaces — grass, clay or hard court, and for indoors.

All the manufacturers would make the same ball, under the same, more exacting specifications. To ensure exclusivity and visibility, they would stamp their brand name on the ball.

Brands used in tournament play include Dunlop, Wilson, Penn and Slazenger. The companies that make those balls were unavailable for comment.