I wasn't there in either case, but I'd say in this case, the guy heard/saw someone taking something from his vehicle. He gave chase, the badguy swung the bag of radios at him, the victim hit back.
Correct, as I understand it.
In the Zimmerman case, did he actually see Martin doing anything? Or just walking thru the area?
Irrelevant. What matters is whether or not Zimmerman was in reasonable fear of his life when he pulled the trigger, and whether or not he complied with the Florida laws regarding use of deadly force in self-defense in all other respects.
Personally, anytime you involve yourself, you're going to be taking some seroius risk. Would I chase after someone who just stole something from my vehicle? I'd say it'd depend on the situation. Of course, if I opt to give chase, then I have to take all responsibility for anything that happens to me.
On a personal basis, that is fine and I agree with it. From a legal standpoint, a victim is allowed to chase a suspect in the same manner a person is allowed to go where he will; even follow and talk to strangers who are just wandering around. There's nothing illegal about it. As to 'taking all responsibility', you know the law doesn't work that way. If I follow you for no apparent reason and you turn and smack me because you don't like me doing that; and if you proceed to beat me to the point where I am reasonably in fear of my life, I can legally defend myself with deadly force. Yes, it was 'my fault' for following you. But I'm still allowed to defend myself from being killed. There is no rule that says "Well, you pissed him off, so you are required to die instead of fighting back."