they were fighting, on the ground with the youth on top. Zimmerman had a head would and bleeding from the nose. Was there a struggle for the gun? Was zimmerman in fear of further severe head injury? etc etc
Stand your ground doesn’t allow you to follow someone then get out of your car and shoot them.
You cannot start a fight and then say you feared for your life. Dang. The kid did not come up to the thug and drag him out of his car.