I've seen some other video's were Smart is trying to imprint his dominance on Brown, in one on one's. Not sure if there is something going on, or Smart thinks he's making Brown "tougher". Smart could also feel threatened by Brown who got the starting nod over him when AB went down. But thats more Stevens wanting Smart run the second unit than Brown out playing Smart.
As of the play, Smart had no right. Brown had the lane, he just took it a little soft. Next season, or even in a month he goes harder and he finishes that play. You have to break the plays once in a while, teams know what they are running by now, it keeps the D honest.