First, a few observations:
The fact that something is legal to do in no way suggests it's the smart thing to do.
Yes, it's legal to ignore the advice of a police dispatcher with training and experience talking to civilians who find themselves in volatile, adrenaline-charged situations, and follow (& perhaps question/confront) an unknown person you believe may be intoxicated and "up to no good," who for all you know may also be armed, all by yourself, and when you have a pretty good idea that the police are already on their way--but I suspect that there aren't more than a handful of law enforcement professionals who would ever recommend it. (Even trained police officers wait for backup, whenever possible.)
I sincerely wish the dispatcher had struck a different tone on that point, perhaps telling Mr Zimmerman in a positive way what the police department wanted and expected from him. (Not "We don't need you to do that." or even "Don't do that." but "Please meet the responding officers at your current location.")
Zimmerman was not a uniformed guard. He was a resident and a volunteer neighborhood watcher. He wasn't "on patrol," he was on his way out to (or back from) the store when he saw the suspicious-looking late teen in the dark hoodie. He did not have any special police or security powers, legally or otherwise. So, while he was legally within his rights to follow, question, or confront hooded strangers in his neighborhood, those strangers (hooded or otherwise) were under no obligation to take kindly to his doing so. And BECAUSE Zimmerman had nothing to denote or identify him as a neighborhood watch volunteer, said hooded strangers who notice a guy following them could easily view HIM as an individual "behaving strangely, and up to no good," as well.
I suspect that neither of them was "up to no good." The whole thing was a matter of two more or less decent people grossly misreading each other, and at least one of them (if not both) making foolish choices based on what they believed about the other. The following is what I think happened. Obviously I'm doing a whole lot of speculating, but I'm pretty sure everything here is consistent with the reported facts and witness statements. (and where the witness statements themselves are inconsistent with each other, I picked, again based on my own speculations.) I am not presenting anything here that goes beyond what's been reported up to now as FACT. As more information comes out, what I believe happened may change. Or I may become more confident in what I believe. As of right now, though, this is what I think occurred...
Zimmerman thought Trayvon was behaving strangely and might be in the neighborhood to commit some crime. He wasn't a bigot out to get a black guy (though I do question how much the fact that the hooded stranger was a black guy played into his profile); he was just a guy who saw something he thought was unusual and reported it. I don't think he followed Trayvon maliciously, either. He just wanted to be able to tell the responding officers exactly where the guy was, and (or) prevent whatever crime the guy intend to commit by being there as a witness. (Most likely, it's the former more'n the latter. I don't think Zimmerman intended for the stranger to know he was being followed, or that he had ANY intention to talk to him, let alone get into anything physical with him.)
Trayvon meanwhile was just a kid coming back from buying a drink at the local 7/11, talking to his girlfriend on the phone, and trying to get out of the rain. At one point (perhaps because the rain got heavier, or maybe because he just wanted a minute's break from it), Trayvon ducked under an awning at the clubhouse. (That's likely a piece of the "strange behavior" Zimmerman witnessed.) At some point though, he notices some heavyset stranger in an SUV watching him, and when he continues down the road, following him in his vehicle. Trayvon walks a little faster. The stranger in the SUV speeds up to keep pace. Trayvon moves off the road onto a walkway. The stranger parks and follows on foot, obviously targeting Trayvon, and likely (in Trayvon's mind, anyway) intending to rob or accost him. Trayvon runs (though apparently not very far). He thinks he lost the guy.
The stranger... (continues following?) (turns to go back to his car?) Either way, Trayvon realizes he hasn't lost the stranger following him, after all. They're close enough to talk--(and at some point between now and the first bit of physicality, become close enough to lay hands on one another.)
One stranger (likely Trayvon) calls out to the other, questioning his motives. The other stranger responds, questioning the first one's motives. Both are posturing, sure they are in the right, and that the other is the creep...
Then one of 'em (and I have no clue which, or why) does lay hands on the other. Maybe it was Trayvon, instinctually realizing that flight didn't succeed, and it was time to stand his ground and fight, rather than lead this creep back to his younger step-brother. Maybe it was Zimmerman, not wanting another to get away, like they always do. Maybe one made some furtive movement the other took as a threat, and pounced in defense. (Obviously, THIS is the whole ball of wax, legally.)
As many point out, every move that each one of them made prior to the initial physical contact was legal--though as many also note, not altogether smart.
If Zimmerman did anything to physically detain Trayvon, or did something to defend himself against whatever he thought Trayvon was about to do, he becomes the aggressor, and Trayvon is justified in trying to incapacitate and escape the guy he thinks is trying to kidnap him.
If Trayvon hit Zimmerman first--even if he thought he was defending himself against whatever he thought was about to happen--he becomes the aggressor, and Zimmerman can rightly claim self-defense.
(I have to say, I suspect that of the two scenarios, Trayvon hitting Zimmerman first, in an effort to avoid imminently getting robbed, kidnapped, or raped seems more plausible to me... ...and that makes me very sad to imagine this kid scared, fighting for his life--and ultimately losing it--over the bad judgement of Zimmerman, and there will be no justice for his family, besides...)
Whoever laid hands on who first, Trayvon got the upper hand. At this point (at least according to my scenario) both men believe they are defending themselves, and fighting for their lives. Once we're here, and regardless of how we got here, I take no issue with how aggressively either man fought. The goal was to stop the other guy from fighting, and live through it yourself. In the end, that is what happened... ...for one of them, anyway...
While Zimmerman may (or may not; I'm not a lawyer) be in the clear legally according to the laws of FL, there is no doubt in my mind that he is far more culpable morally than Trayvon Martin. As I've said before, this whole thing took about five minutes. Trayvon spent most of that time avoiding the "dangerous stranger" he encountered, while Zimmerman spent most of that same time moving closer to the "dangerous stranger" he saw.
A whole lot of what Zimmerman did, while all legal, served to amp up and inflame the situation.
(Please don't tell me that everything George Zimmerman did was legal. I know. It was all legal. But at least some of it was profoundly stupid, too.)
He went against the advice of an experienced law enforcement representative.
He went against the guidelines of pretty much every neighborhood watch program.
He went against the common sense of many gun owners. (You don't go out looking for trouble or willingly walk toward it, gun in hand (actually or proverbially), unless you are defending a life.)
Up to the point where Trayvon Martin took that first swing--IF he actually was the one who took that first swing--he did nothing illegal.
He did nothing to amp up the situation.
He tried to avoid the trouble he thought was coming for him.
And he didn't do anything I could identify as stupid, either.
Again, this is just speculation, based on the reports currently available. If you don't agree with me, fine... But simply saying it's just speculation is nothing more than stating the obvious. Instead, tell me why you think I'm mistaken, and correct my mistake(s) with your own fact-based speculation.
I believe the smartest course for Zimmerman was to wait to meet the responding officers. But if he really could not bring himself to do that, I think (with all the brilliance of that 20/20 hindsight, obviously) that everyone would've been better off if Zimmerman had been more assertive (and/or a little more devious). Instead of skulking behind Trayvon in his car and then on foot, he should've gone straight up to him and either:
1) identified himself as a guy from the neighborhood watch, said that he recognized most of the people who lived in the complex and explained that he thought Trayvon looked lost, and offered to direct him to where he was going... or
2) taken off his watch and gone up to Trayvon and asked him for the time (or perhaps said that HE was lost, and asked Trayvon for directions, or something similar).
I mean, I understand that Zimmerman probably had no idea how much he was freakin' the kid out, but he was almost certainly freakin' the kid out, the way he chose to handle his surveillance...
Anyway, that's my educated guess as to what may've happened, and I'm stickin' with it until some fact blows a hole straight through it (at which point I'll rewrite it, based on the new fact(s) available.)
UPDATE: Hey, lookie here!! Someone else (Julian Sanchez) wrote this post before I did, and came to very similar conclusions: Tragic Scenarios