Swim Star Riley Gaines 'Ambushed,' 'Physically Hit' In Conflict W/ Trans Activists

Swimming star Riley Gaines says she was attacked by protestors on Thursday night and forced to barricade inside of a college classroom for hours ... after she gave a speech arguing that transgender athletes shouldn't be allowed to compete against biological females.

The heated confrontation went down at San Francisco State University's campus in Northern California ... where Gaines had arrived to speak with students at a Turning Point USA event.

In her chat with a small gathering inside of a classroom on campus, Gaines -- who famously spoke out against the NCAA and transgender swimmer Lia Thomas earlier this year -- explained why she believes trans athletes have an unfair advantage over biological women.

But, minutes into her talk, she was interrupted by a group of protestors ... who only got louder and louder throughout the night.

Eventually, Gaines said as she made her way out of the classroom ... trans activists who had entered the building to object to her stance attacked her.

"I was ambushed and physically hit twice by a man," she said of the scene on her Twitter page. "This is proof that women need sex-protected spaces."

Gaines shared a video of her encounter with protestors inside of the SFSU campus building ... showing her in a blue sweater being ushered to another classroom by police as people hurled chants and insults at her.

SFSU's student-run media outlet, the Golden Gate Xpress, reported Gaines was forced to stay locked inside of the classroom with police protection for roughly three hours.

Cops ultimately ordered people to disperse -- and Gaines, a former swim champ at the Univ. of Kentucky, was able to leave safely.

Gaines' agent, Eli Bremer, blasted the protestors in a statement to Fox News Digital after the event ... saying, "It is stunning that in America in 2023, it is acceptable for biological male students to violently assault a woman for standing up for women’s rights."

Bremer added, though, it would not impact Gaines' decision to speak out going forward.

Caitlyn Jenner voiced her support for Gaines after she became aware of the incident, writing in a tweet, "Pray for Riley Gaines! You are a courageous voice of reason, an incredible athlete, and beyond brave. Praying!!!"

We've reached out to both SFSU officials and the San Francisco Police Dept. for comment on the matter ... but so far, no word back yet.