Zimm never assaulted ashtray. V
Even if Trayvon stopped running, and turned to see Zimm trying to tackle him/all wide eyed ready to move on him - the black kid would be justified in punching him in the jaw.
So here's 2 likely scenarios, which I believe both paint Trayvon as a victim:
1. Trayvon swings for Zimm in defense and they brawl (both trying to aggresively defend themselves) T get's shot. Agg Assault/Murder
2. Trayvon stops running and turns to Zimm, Zimm throws the first punch - Agg Assault/Murder.
I can't see Zimm's innocence in either.