There is a section in the Bronx that is private, anyone can drive on the roads, but they are responsible for their own plowing, garbage, paving etc... They hire their own security. I am a runner and I used to leave my apartment at night (when it was cooler) in the summer to go for a run. When I first started doing it I would notice that I would be followed by the security guards in their car. I knew what they were doing and it didn't bother me because they were just doing their job and protecting the neighborhood they were hired to watch.
Never once did I confront them. After a while, I guess when my face became familiar they stopped following me.
The point is, even is Zimmerman did get out of his car while on the phone with 911 after he lost sight of Trayvon, if Trayvon came at him, he had every right to defend himself.