Olympic gymnastics champion Simone Biles has called former US swimmer and activist Riley Gaines "sick" over her online comments about a transgender woman softball player. Gaines, who has been vocal about transgender women athletes competing in women's sports, mocked the Minnesota State High School League for removing comments on their post about the Chaplin Park girls' team celebrating the State Championship. Chaplin Park's team includes a transgender woman player.

"You're truly sick, all of this campaigning because you lost a race. Straight up sore loser," Biles wrote on X. Gaines tied for fifth place with transgender woman Lia Thomas in the 200m freestyle swimming at the 2022 NCAA Championships.

Later that year, World Aquatics voted to stop transgender women from competing in women's elite races if they have gone through any part of the process of male puberty. Thomas has since failed with a legal challenge to change the rules.

"You should be uplifting the trans community and perhaps finding a way to make sports inclusive OR creating a new avenue where trans feel safe in sports. Maybe a transgender category IN ALL sports," continued Biles. "But instead... You bully them... One thing's for sure is no one in sports is safe with you around."

Biles, a seven-time gold medallist, has been an outspoken campaigner for mental health awareness throughout her career. She withdrew from the women's team final at the Olympic Games in Tokyo in 2021, as well as four subsequent individual finals, in order to prioritise her mental health.

Gaines responded to Biles in follow-up posts, saying the gymnast's stance was "so disappointing" and that she should not be advocating for transgender women in women's sport with her platform. Since tying with Thomas in 2022, Gaines has said she felt "cheated, betrayed and violated". She has become an advocate for banning transgender women athletes from competing against women and girls.

In February, Gaines was present at the White House when United States President Donald Trump signed an executive order excluding transgender girls and women from competing in women's sports. In April, judges at the UK Supreme Court ruled that a woman is defined by biological sex under equalities law.

Since that ruling, a number of UK sporting bodies, including the Football Association and the England and Wales Cricket Board, have banned transgender women from playing in women's sport.