On Wednesday afternoon, an 18-year-old man was attacked and robbed while riding the J-Church. Somewhere between the Glen Park and Balboa Park stops, it seems, the teen was "knocked unconscious by a man with a knife." The suspect then ripped off his backpack, punched him again, and then elbowed the victim before fleeing.

The jerk swiped the guy's "backpack, laptop and portable game system." Suspect is described only as "a Hispanic man between 20 and 25 years old."

Anyone with information should call the SFPD the anonymous tip line at 415-575-4444 or Text a Tip to TIP411 and begin the message with "SFPD."

[CBS SF]