You would make contact, established. So, since we're doing "what if's" all over these Zimmerman threads, who's to say that's not exactly what Martin did? What if he didn't just hop out of a bush to blindly ambush Zimmerman, what if he walked up and asked why he was being followed? Seems believable. What if he started laying out the beating because he felt threatened and saw it as his only miens of self defense? What if a nervous Zimmerman tried to draw when confronted by such a suspicious person, and Martin thinking he was being attacked hopped on Zimmerman to prevent what he thought would be his bodily harm?
We have no idea what went on. We never will.
Believable? Possibly. Based on Martin's own history and internet posts, I certainly don't find Zimmerman's version less believable. More so in fact. Even if Zimmerman challenged Martin, it's still on Martin if he threw the first punch. That's what the jury believed, even if they did think Zimmerman was an idiot.