The 2018 U.S. Open was Naomi Osaka’s first Grand Slam win, but much of the talk after the match was about Serena Williams ‘argument with the chair umpires. The tennis icon was candid about why she got so upset in an essay for Harper’s Bazaar on Tuesday. 

At the U.S. Open, Williams called the umpire out for what she called sexist behavior after he penalized her for being coached. When she said she wasn’t being coach, the umpire then penalized the tennis star for her reaction.

In the new essay, Williams defends that reaction.

“Ever since I was a little girl, I’ve felt a need to voice my opinion and be heard… And I won’t ever stop raising my voice against injustice,” she wrote. 

Knowing this was about more than what happened on the court, Serena say it as an opportunity to speak up on the issue of sexism. 

“I was hurt—cut deeply… for some reason I couldn’t shake the feeling that this was about so much more than just me,” she said. 

She opened up about being a good example for her daughter and teaching her to speak up for what she believes in as well. 

Williams admitted the controversial call left her with sleepless nights, with many of those nights thinking of the young tennis star who beat her.

“Not only was a game taken from me but a defining, triumphant moment was taken from another player, something she should remember as one of the happiest memories in her long and successful career,” Williams wrote about Osaka.

She added that she questioned herself, and questioned how it could have been handled better:

“My heart broke. I started to think again, ‘What could I have done better? Was I wrong to stand up? Why is it that when women get passionate, they’re labeled emotional, crazy, and irrational, but when men do they’re seen as passionate and strong?'” she asked.

Staying true to her open approach, Williams admitted it was difficult to go back to playing tennis and that she started seeing a therapist following the match. That led to her realizing the best way to move on was to apologize to Osaka. 

Williams wrote a letter to Osaka, and in it said she wish she could “live that moment over again.” When Osaka responded, Serena said she got emotional.

“When Naomi’s response came through, tears rolled down my face,” Williams said. Osaka wrote that Serena “misunderstand anger for strength” and added that Williams should simply “continue trailblazing.”

Williams knew after reading Osaka words why she had struggled so much following the U.S. Open:

“I had felt that it was my fault and that I should have kept my mouth closed. But now, seeing her text putting everything in perspective, I realized she was right.”