I think so much of this case and the reaction to it comes down to two segments of American society being on different pages about some key issues.
One segment believes that any sort of physical assault is uncalled for, completely over the top, dangerous, terrifying, heinous. The law agrees with them, because this segment wrote the law. This segment upholds and enforces the law.
The other segment has a much higher comfort level with brawling and punching someone for dogging you, disrespecting you, eyeballing you, whatever. People raised within this segment grow up having a very different understanding of when violence is acceptable, and what sorts of behaviors, words, actions can be considered valid provocation to violence.
There are some white people in the second segment, and there are some black people in the first segment, but they represent a minority within each of their racial groups. (Think Kid Rock and Bryant Gumbel)
So I guess we can chalk this up to another cultural point of difference much like y'know, whites can't jump, dance, have no rhythm, talk differently... and a million other things like that which black comedians get a lot of mileage out of.
I think if you walked up to a lot of black youths, and asked them whether a white person would tend to call cops quicker and for lesser events than a black person, they'd agree wholeheartedly. Then they'd punch you.
This gets at what I'm talking about. Segment 1 views police intervention as more of a positive and necessary thing than Segment 2 does. Segment 1 will invoke the rule of law and the police much more quickly. For a much wider variety of things.
In Segment 2, calling the cops for a "simple" beatdown or "fight" is unthinkable.
I think GZ was firmly in Segment 1, and his interpretation of what was going on was rooted in that. His reactions, from calling cops to using his firearm, were based on Segment 1 thinking.
I think TM was raised in a family that was closer to Segment 1 than a lot of black families, but by no means fully within it. I think TM rebelled against whatever level of Segment 1 thinking HAD taken root in his family, because he associated it with being a pussy, acting white, and being a little bitch. He wanted to be hard, tough, and intimidating. He wanted to style himself as a thug and a gangsta and a criminal, and sought to embrace Segment 2 thinking more than his older half-brother appears to, more than his mother appears to, and in a way I suspect is more in line with how his father USED to be some years ago (Removed gang tattoo after first couple press conferences, etc.)
I think TM probably thought of attacking GZ as a fairly justified reaction to disrespect and calling cops on him, which I believe he knew GZ had done. I think his intention was to knock GZ out with that punch, and he improvised very poorly after that didn't happen.
They were on different pages. But it's not just a toss up, Segment 1 thinking = continued civilization we'd all like to live in, if too many people start being on the page of Segment 2 thinking... civilization turns into a festering pile of shit, one big Detroit.