If you're Brown and you've already, according to the account, been shot once in the arm in the struggle for the gun and then have gotten away why would you stop, turn around, and "bum charge" the officer who still had the gun?
Why would you break store windows out, run in and steal items, then set fire to the place, all while the MEDIA had cameras on you and the POLICE were standing there watching ?
Mr. Brown had an audience. It was his 'hood'. It was his 'reputation'. His friend was daring him.
There are many different reasons for Mike Brown's behavior, just as there are for the behavior of the Ferguson 'protestors'.
The 'reasons' aren't necessarily 'logical'.