I think that ends up being the key question-- are you allowed to shoot someone who is unarmed (though they just tried to take away your weapon and use it on you) but is rushing at you to attack you (who is 6 foot 4 and about 300 lbs) or are you not?
Since Brown had already committed felonious assault and battery on the police officer, the cop had every right to use whatever means necessary to defend himself from a second attack and to stop the felon from escaping and potentially putting innocent people in the neighborhood at risk of being his next victim.
If he has already tried to get your gun from you, absolutely, drop him.
Yes, yes you are.
Supreme Court rules back in, what, the 70’s, that physical size is an affirmative defense for the use of deadly force. . .police or not.
Somebody clearly as large as this thug was coming after you, you can’t reasonably be expected to engaged in hand-to-hand combat with the thug. . .think Zimmerman.