From your link...”Details are slowly emerging which indicate Brown and his pal Dorian Johnson initiated a confrontation with a police officer responding to a call. Brown severely beat the officer and caught a round as a result. When he charged the badly beaten officer a second time, he caught a few more.”
I understand photos of the officers face lacerations etc. will be eventually released.
Their definition of "severe" might be different from ours but if a 300-pound guy smacks you just once - it might be enough.