The short answer: Grand Slams play by different rulesWhile the ATP and WTA govern their respective tours, Grand Slams fall under the International Tennis Federation. And according to Tennis Australia, wearables like WHOOP are not currently permitted during Grand Slam matches. Sabalenka said she had received written approval to wear the device and couldn’t understand why Grand Slams hadn’t reached the same conclusion as the tours. Tennis Australia says discussions are ongoing, but until something changes, umpires are enforcing the rules as written. Man of Many has contacted Tennis Australia for comment on the ruling around player-worn wearables at the Australian Open.