A witness spotted a hand grenade at about 5 p.m. being juggled by a performer on the 300 block of Jefferson Street, San Francisco police Lt. Troy Dangerfield said.
Responding officers detained the performer, a man whose identity has not been released, and closed off the block while a bomb squad investigates.
As of 6 p.m., Dangerfield could not say when the block would be reopened.
