The only place George Zimmerman could back up was into the sidewalk.
Officer Ironman had all sorts of options, after he provoked the ensuing trouble.
And, BTW - Zimmerman didn't provoke the fight...
Neither did Michael Taylor.
Some would say that Zimmerman did provoke it, by following Martin and by verbally confronting him.
That's nonsense, since Martin could have decided to either respond or ignore Zimmerman - he did not have to assault him. That was his choice.
Likewise, Taylor verbally confronted Fischer.
Like Martin, Fischer could have chosen not to physically attack his interlocutor, but he did.