content: This is all part of the Oakland thug stuntin/sideshow "culture".  They like to do this on the weekends early early morning ect.  Its a well known thing if you live around the bay in CA.  You are right, these are 100% stolen, kinda suprised they all had helmets, usually not all of them do.  They do this shit in groups because they feel they wont all be arrested or caught.  I have heard that some go full Road Rash style, with chains and weapons to hit cars.  Its just mayhem which these monkeys call "fun".  Ive often wondered what would happen if a motorist hit one, out of fear or whatever, and its an unlicensed stolen dirt bike on a freeway?  Its CA so I imagine the motorist would be in some trouble, which sucks because these people are clearly out causing mayham and terrorizing the public.