One thing is that evidently a moving vehicle struck an officer -- but it's not clear whether or not he was on foot, and how hard he was struck
The nightmare scenario, or one of them, is that the guys undercover thought they'd been made and panicked.
The 31 shots is not so remarkable. Once the lead starts flying, the evidence shows that most gun fighters empty their magazines without even knowing it.
A lot of good studies are coming out about what happens in a gun fight, and it's not what most people think -- including what looks like a shot in the back. (Whoever put that last paragraph in the article needs to have every mistake he's made publicized also.) It is entirely possible that between the time the irrevocable neurological commitment to pull the trigger is made and the time the trigger is actually pulled, the target can swivel. It is psychologically rare, once the firing begins, for someone who doesn't fight a LOT (or play video games a lot), to stop shooting when he sees the target spin away.
But all that aside, this is not looking very good right now. Of course we can rely on Sharpton to make a righteous shoot a cause celebre just because rousing the rabble is what he likes to do.
I had read one article that said one of the officers emptied two clips. It looks bad.
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You watch too much TV.
Far more likely (@ 1,000,000%) is that the UC heard the remark about getting the gun and sensed a drive-by in the making. The guys in the car had been arguing outside the spot with the bouncer and some others over whether one of the girls was going to give all of them a happy ending to their party. It was then that the 'get my gun' remark was made.