Robb Allen provides the backstory on this one:

The backstory is that the firefighter was drunk and had assaulted a cab driver already. The cop was working security and went to apprehend the guy who then resisted arrest. A guy decided to video the incident because he wanted to capture the cop being all brutal and whatnot, but in the end his video was proof enough to a grand jury that the cop’s shoot was justified.

Make sure that you follow that link, as Robb does one heck of a job articulating the cultural issues at play (which I suspect will play out in the comments here as well).

This officer was punched hard in the face probably four or five times in the course of 2-3 seconds before he fired his weapon to defend his life.

Now, contrast the brutal last 5 seconds of that video against the 911 call audio evidence that George Zimmerman screamed for help for 40 seconds. He went eight times as long before he fired.

Now that I have a frame of reference for that, I’m frankly amazed that Zimmerman waited as long as he did before he shot Trayvon Martin.