The stabbing was reported at 9:50 p.m. at the corner of Eddy and Hyde streets.
Police said five people were harassing a homeless person when a 31-year-old man intervened to stop the harassment and was assaulted before being stabbed with a knife.
The stabbing suspect was described as a 16- to 20-year-old male.
The victim was taken to a hospital with injuries not considered life-threatening.
Police said they did not have any description of the four other suspects. They ran away, heading west on Eddy Street, according to police.