The attack was reported at 8:50 p.m. and the victim said it occurred somewhere between the Richmond and North Berkeley stations, BART
police said.
The suspect then fled when the train stopped at North Berkeley and has not been located. He was described as a black man in his 20s who is about 5 feet 6 inches tall and wore a hooded sweatshirt, according to police.
No other information about the case was immediately available from BART police.