Who knows? But even if we assume Trayvon hit him with a fist or elbow it means nothing. Likewise, even if Zimmerman bonked his nose on the sidewalk it means nothing. No one is disputing that some kind of physical altercation took place.
What I find interesting is that Zimmerman never attempted to defend himself in any way, he never hit Martin or scratched him, he never bit him, he claims he was fighting for his life against a suddenly homicidal maniac, a guy he claims told him he was going to kill him, and he never did any of that. He just shot him.
And by the way...
How LIKELY is it that Martin, who has no history of violence and multiple character witnesses who have spoken up about his laid back nature, would suddenly attack someone and tell them that he planned to murder them?
That's what Zimmerman claimed. He claimed that Martin told him he was going to murder him. Does that seem plausible?