Bill Logan commented:
"NO gun was INTRODUCED......Z was on the ground being relentlessly PUMMELED per EYE witness.......tra von HAD THE LEGAL DUTY to STOP the ATTACK once the other party becomes defensless....HE DID NOT and was subsequently in the midst of an assault and battery."
Obviously, the other party (Zimmerman) wasn't defenseless enough... He was fully able to shoot and kill Martin. Trayvon Martin should've been armed (so he could "stand his ground" and defend himself against the creepy stranger who was following him) or he should've knocked that man clean out, so he was no longer in danger of bodily harm (like being shot, fer'instance.) Once you commit to physically defending yourself against someone you believe intends to grievously harm you, you don't stop until you're sure your attacker is incapacitated enough so that s/he can no longer do so. (If George Zimmerman took any classes on using his weapon for self-defense, he was likely taught the same. Once you've committed to using your weapon to defend yourself, you don't shoot to wound your assailant.)
My take is that they were both innocent, but each believed the other guy was dangerous, based on actions (and maybe a touch of distrust for someone ethnically different from them, as well)... If Zimmerman had just stayed in his car and waited for the responding officers like he was instructed to do, neither man would've been in any danger from the other or suffered any injuries, and both would be home with their families today.