Multiple gun shots were fired around 5:15 p.m. on the 1000 block of Market between 6th and 7th streets, Sgt. Dennis Toomer said.
One person, a man in his 20s, was struck by shrapnel and was taken to San Francisco General Hospital with non-life threatening injuries to his head.
It is unclear if the victim was the intended target, Toomer said.
Police arrested a suspect, described only as a black male in his 20s, and recovered a weapon allegedly used in the shooting. The suspect's identity has not yet been released.