Earle,
It's called the Castle Doctrine:
http://en.wikipedia.org/wiki/Castle_doctrine
It states you are no longer required to retreat in your home before defending yourself against harm.
Then of course as you said....that evolved into "Stand Your Ground" for outside your home because it was so difficult to determine what is reasonable to expect to retreat from a harmful confrontation.
At the bottom of this page there is more detail on which states apply these laws.
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My personal take on this case is it may boil down to whether GZ was assaulted by TM while on his way back to his vehicle or somewhere else - but NOT WHILE following TM anymore. Because when the 911 operator said "We don't need you to do that" - his reply was OK.
I think it's entirely possible to speculate that TM may have initiated and/or escalated the confrontation to the point where physical contact was made and things went south very quickly.
So I wonder who it was that threw the first punch? And wouldn't that be the "clincher" as to whether or not GZ should be help liable?
As Audio mentions....following someone - even making them feel uncomfortable...is not against the law.
Once fists fly - the person who throws the first punch should be help accountable. Regardless of anything else.