From what I've read it sounds like the boy was the one exercising self defense "stand your ground" and bit off more than he could chew (a man with a gun) and the man with the gun then defended himself from the situation he perpetrated.
The lesson seems that both applications of stand your ground were ill-advised.
For both, it would have been better to exit the scene (although the 911 tape which I have heard seems to indicate that one individual precipitated the encounter onto the other).
What will never be known is the whole 'first blow' thing. Invading a persons space verbally is largely protected speech, striking them for it (if that occurred) is assault, and shooting the striker is, it seems, under FL law, self-defense.
Now, if the gun-man grabbed the kid first, then the gun-man is the attacker, the kid defended, and the gun-man upped the ante, in which case it is murder where I come from.
The actual facts will likely not be known. The matter of pursuit of the kid indicates who initiated the encounter, the specifics of how that encounter developed would determine fault, and that portion it seems is rather blurry.
Since the gun-man brought it all about, in effect looking for trouble IMO, seems like manslaughter.
From about a bazillion miles away that is.
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