A 15-year-old boy in San Francisco was beaten unconscious by a group of 18 men after he spun a soccer ball in front of one of their faces, police said Monday.

The attack, which police are investigating as an aggravated assault, happened Friday about 10 p.m. on the sidewalk in the area of San Bruno and Silver avenues, next to the Highway 101 overpass, said Officer Carlos Manfredi, a spokesman for the San Francisco Police Department.