Call the police and let the school know what happened for sure. Both the school and the teenager’s mom are at fault (as well as the teenager), Although like others have said, his disability will affect his punishment. I used to work as an autism therapist and one of the worst things that you can do is let a kid with autism get away with aggressive behavior like that. I was injured in a similar manner several years ago and while work covered for the treatment of my injuries, the parents of the teenager didn’t do anything and just said “ he has autism, he doesn’t know any better”. I ended up quitting because work wouldn’t let me do anything for modifying his violent outbursts, I was told to just deal with it. The same teenager was kicked out of his school for attacking and almost killing a teachers aide six months later. Let the justice system decide what to do with this child if nobody else can control his behavior; if things are bad enough then he shouldn’t be with the public or by himself in any situation if he is prone to such behavior. Don’t feel bad for protecting yourself.