Grizzly bears? come on.
He may have tried to get the gun away. I'm assuming everything in the cops favor on that. Even after I do that, the cop had the gun and had it aimed at an unarmed person. There is no more threat after that, certainly not one justifying lethal force.
God forbid he try to figure out the guy's age. Shoot first, ask questions later, amirite? And no, when the 6'5", 300 lb person is unarmed and you have a gun aimed at them, I don't think their size alone justifies the use of lethal force.
As I've done in the past few pages here, assuming Brown did try to wrestle the gun away from the cop, Brown didn't get the gun. The cop fought off the 6'5", 300 lb guy from getting his gun, he pulled it from the holster, aimed it at Brown, and shot him 6 times. If he was a physical threat, the cop would probably know hey, this 300 lb guy doesn't know how to handle himself... he probably knows the guy is at least very immature physically. The cop has the gun, it's in his hand alone... Brown is no longer a threat justifying lethal force. If he could fight Brown off of his gun, he could likely take him down and cuff him. At the very least, he could have shot him in the leg, disabling him... then ask questions about his age, ID, etc.