The problem is that Zimmerman did not just ask Martin questions.
Knowing the neighborhood, Zimmerman ran south and east while Martin walked east and then south, so Zimmerman had cut him off and was blocking his way. Being dark out, that is a very intimidating thing for Zimmerman to do.
Martin did not know Zimmerman had a gun, and no one knows who started the physical fight.
You are assuming Martin started the fight, and I doubt that since at Martin's age, they don't yet really know how to fight.
Zimmerman had over 100 pounds on skinny Martin.