I’m not certain which state you practise law, but I practised in VA and there is evidence that in VA he would not be prosecuted.
If the facts show that Zimmerman’s head was being slammed into concrete and Zimmerman did not initiate the first physical contact, then he can use deadly force to defend himself in VA.
I was a Prosecutor in Fairfax County, VA for 25 years. Absolutely it would be prosecuted.