A man pursued a robber on foot for more than a mile to the Mid-Market district before he was stabbed in the back on Wednesday, police said.

The robber approached the 25-year-old man at the corner of California and Polk streets about 6:15 a.m. and demanded all his money, Officer Albie Esparza said.

The victim protested but eventually gave up his cash and phone. The victim, however, didn’t want the crook to get away. With help from an unknown witness, he trailed the bandit roughly 15 blocks.

A brawl erupted between the three men near Market and Seventh streets, Esparza said.

Police responded and the victim was taken to San Francisco General Hospital, where he realized he’d been stabbed. His injuries, which included facial lacerations, were not life threatening, Esparza said.

Meanwhile, a suspect was arrested at the scene of the fight. Terrence Watkins, 45, of Emeryville, was booked on charges of robbery, assault with a deadly weapon, possession of stolen property, and resisting arrest.

The bystander who helped the victim vanished before police could interview him, Esparza said.