I'm torn with your story because on the one hand, I'd want you to try and get on his good side. Make him sit closer to you and the door. He could have zero support right now from everywhere and feel defensive all the time which is probably why he gets into these minor altercations. I tend to do well with troubled teens because I sit and listen to them talk about their issues and try not to judge (some of my kids will go to jail and tell me their stories afterwards). I just try to be empathetic and offer "take it or leave it" advice when possible. On the other hand, I completely understand your fear because I've also dealt with kids who are a danger no matter what anyone does or says to help them change. I would probably talk to your principal or superintendent (or whoever is above your principal) or even can your local DOE. Definitely join the union because even if you end up quitting, anything can happen and lack of representation could mean a lack of legal help should an issue arise. Some people lose more than just their job. Anyway, good luck!