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At least three members of the Baker's Dozen a cappella group were hurt. One suffered a broken jaw.

No arrests have been made. Police said they are investigating.

The trouble started when a couple of partygoers began mocking the 16 student singers -- who wore sports jackets and ties -- as preppies, witnesses said.

"You're not welcome here", Sharyar Aziz Jr., an 18-year-old Baker's Dozen member whose jaw was broken, quoted one partygoer as saying. "He called a few members of the group, whether it was fag or homo, very, I would say, juvenile taunting."

Reno Rapagnani, a retired San Francisco police officer whose daughter hosted the event, shut down the party. As the singers headed back to a nearby home where they were staying, another group of young men got out of a van and jumped them, according to Rapagnani.

"They were surrounded, then tripped -- and when they were on the ground, they were kicked", Rapagnani said.

Two other Yale students needed medical treatment following the fight, one for a concussion and the other for cuts and a swollen ankle.

Police said they arrived and found about 20 people fighting in the street. They interviewed some of the participants but let them go after taking their names.