Any teens.
If a security guard tries to question or detain you, you don't get into a fist fight with them. That's just stupid and escalates the situation. Note, I don't think Zimmerman has any business carrying a loaded weapon (imo a tazer is probably all he should be legally able to carry as a community patrol, that is if America's gun laws weren't so retarded).
There is a little problem with your analysis; usually, security guards detain people in connection to very specific, very obvious situations (like, I don't know, a mall, a public function, something where people can actually know that this person has authority over this location). Here, you have a kid walking through a neighborhood, get's stalked by a stranger, tries to run away, and continues to get pursued by the same goddamn stranger. These aren't even disputed facts!
But no, Mr. Security Guard Z has such apparent authority over the neighborhood. Too bad he seemingly didn't let the kid know that.