He jumped on the hood of a car? Not the most tactical maneuver I've ever seen, but whatever works I guess.
The guy the officer was going against had an assault rifle just as, if not more, powerful then his AR. Staying in the car as you pull up and try to exit is sure to get you killed. Theres a few other videos around with officers stopping the car, getting out, and leaving it in drive as it still rolls using it as cover as they shoot from behind it, or in front of it.
Stupid looking, but it sure as hell gets the job done when you need to dismount quick.