How's this for an only-in-San Francisco story:

Members of the Baker's Dozen, the renowned, all-male a cappella singing group from Yale, are pummeled outside a New Year's Eve party after singing "The Star-Spangled Banner."

. . .

The 16 singers showed up late to the party wearing preppy sport jackets and ties, and launched into "The Star-Spangled Banner."

A couple of uninvited guests started mocking them, and allegedly the words "faggot" and "homo" were tossed -- and so were a couple of punches.

The loud noise drew relatives from next door, who promptly ordered the house cleared.

The Yale kids, most of whom were staying with a family a block away, began heading home.

But witnesses said one of the uninvited guests -- who happens to be the son of a prominent Pacific Heights family -- pulled out his cell phone and said, "I'm 20 deep. My boys are coming."

According to Rapagnani and others, the Yale kids barely made it around the corner when they were intercepted by a van full of young men.

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

According to police reports, the cops arrived about 12:40 a.m. to find 20 people fighting in the street.

To the police, who were out in force to keep a lid on New Year's, it looked like just another drunken brawl.

But according to Rapagnani, "This was not a fight -- it was an attack."