San Francisco man surrounded, attacked by teens outside Mission apartment

(image from Google Maps) 

A San Francisco man suffered a serious head injury when he was knocked to the ground by a group of teenagers who surrounded him outside his Mission District apartment building on Monday afternoon, police said.
The 54-year-old victim was surrounded by a group of seven to 10 boys between 15 and 18 years old outside of his apartment gate in the 1800 block of 15th Street at about 1:30 p.m., according to police.
The teens started an argument with him, and while he tried to get through the gate to his building, one of them punched him in the head and he fell to the ground. He hit his head and was knocked unconscious.
The victim was still unconscious when he was taken to a hospital with head trauma. His injuries are considered life-threatening, police said.
The suspects remain at large and police did not provide a more detailed description of them.