I didn't say he was trying to fight cops, I said he heard a car, or, better put, he heard a sound that seemed threatening and in the few seconds the situation lasted, he reached for the gun as something to swing in case someone was trying to do something to him. If I heard a car coming up behind me that shouldn't be there and I had something on hand to potentially swing around, I'd probably reach for it too.
Also kids don't tend to listen to stuff like common sense. Yeah, it was stupid of him to even have something like that on him, especially since it looked real enough to warrant a call. At the end of the day though, the kid was stupid. He didn't need to be shot just for being stupid like most kids are. As for the sliding thing, why were the cops even driving on the grass? And even if that does explain why they were so close, why start shooting immediately as you get out of the car? That guy shouldn't have been a cop, as we've seen from his files and what not, but even still, three seconds is not near enough time to accurately assess what's happening. I could keep typing, but my point would eventually end up as saying the cops are still entirely to blame here (not that you're saying anything differently from that, at least as of that last post you made). That guy shouldn't have been on duty, they shouldn't have driven on the grass if their car wasn't equipped to drive on it, at least not until they assessed the situation and considered Tamir a viable threat (as in, they can drive all over the grass if the kid really was a problem/shooter), and they shouldn't have opened fire right when they got out of the car.
The kid was stupid, but the cops were more than stupid. That ended up costing an innocent life.