Gaines' extensive history of attacking transgender (and cisgender) women in sports led Biles to call her a "bully" in an X post.

"I believe sports organizations have a responsibility to come up with rules supporting inclusion while maintaining fair competition," Biles said in a post on X.

Simone Biles and Riley Gaines traded social media barbs over the latter's recent comments advocating for the exclusion of transgender athletes in women's sports.