The 22-year-old victim was walking near 26th and Bartlett streets at about 3:45 p.m. when he was approached by three suspects. One pulled out a black handgun and struck him in the face with it, according to police.
The other two suspects stole the man's cellphone and backpack and ran away. They had not been found as of Tuesday morning, police said.
The victim suffered a bruise to his face but declined medical treatment.
Anyone with information about the robbery is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.