The graphic video has been viewed by dozens of students at the school after it was shared by members of the varsity baseball team.
The victim: a 15-year-old junior varsity player.
"In the video, he's choked out almost to the point of not being able to breathe, and while he is on the ground being photographed, made fun of, they were pretending to sexually assault him a couple of the other varsity members," attorney Elan Zektser said.
Zektser provided Eyewitness News with the video. He represents the family of the teen, which has filed a claim against the school district and baseball coach.
"The district and the coaches knew what was going on in the school, and that is that there was severe hazing, assaults, sexual assaults happening in the varsity locker room," Zektser said.
A divide, Zektser said, was created by a culture that allowed only varsity players access to the locker room while younger players had to use the dugouts.
The incident happened in February, but it wasn't until April that the victim's family would learn of the video.
"I was obviously devastated. As a parent you don't ever want to hear that and then to find out the school already knew this and didn't even tell me - it was heartbreaking," the victim's mother Priscilla Villanueva said.
In response to Eyewitness News, the Upland Unified School District released a statement that reads in part:
"The district launched an internal review of the alleged incident involving physical misconduct by players on the UHS varsity baseball team."
Villanueva said she has since pulled her son out of school due to fear of retaliation.
"My son loves baseball. He's played since he was 6-year-old. That's his passion, that's his outlet. That's what he loves," Villanueva told Eyewitness News.
"Literally overnight that was taken from him," she added.
The school district said it could not comment on the victim's claim due to confidentiality reasons. It also said that it is committed to student safety.