Everytime they compete, female athletes challenge societal norms of femininity, submissiveness, and broader gender roles. They challenge the masculine domaine of athletics, asserting qualities like power, competitiveness, and ego that weren't favored in women just a half-century ago. So when we see college softball players built like a tank, Candace Parker dunking, or Brittney Griner wearing a men's suit, some will think, "oh, those are just some lesbians."
There's nothing wrong with an athlete (or any person for that matter) being gay, but trying to out a female athlete on the basis of their athletic prowess and attaching a negative connotation to their status is wrong. While it's true that some female athletes are indeed gay (no different than the overall population), it's important to not let participation in athletics be a guiding force for assuming the sexual orientation of a woman. That's a dangerous and insensitive path to go down for the athletes involved and the LGBT community as a whole. Plus many women athletes are in heterosexual relationships. WNBA player Moncia Wright just got engaged to Kevin Durant, so there's that.