A patrol officer tried to make an "investigative stop" of Foster, who was riding a bicycle at Marin and Florida streets in an unsafe manner around 7:40 p.m., Lt. Kenny Park said.
Foster fled on foot and the officer chased him, then a "violent physical confrontation" between the two ensued in the 400 block of Carolina Street, Park said.
The officer fired his Taser stun gun but it was ineffective and Foster forcibly took away the officer's metal flashlight and "presented" it in a threatening manner, Park said.
"The officer, fearing imminent and serious physical harm, discharged his duty firearm, striking the subject," Park said.