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.
When Joakim Noah was a rookie in Chicago it's been well documented that Ben Wallace went at him every practice, never giving him in an inch and probably taking it too far regularly. The very next year Joakim Noah is going toe-to-toe with KG not taking an inch from him because if he could handle the abuse from Ben Wallace he could handle it from anyone.
Smart isn't being as bad as Wallace was to Noah but that kind of competitive nature is valuable in practice. Crowder and Smart made it clear this summer that Jaylen wasn't going to just ease his way onto this team. We had a tough minded defensive culture and if the rookie thought he was just going to come in and do things his way he was in for a rude awakening. To Jaylen's credit he responded.
Now look at Jaylen, he's referring to games big games as bar fights and saying Steph Curry's antics are cute. He feels comfortable speaking his mind and going against the best because he's paid his dues in practice and can hold his head high that he is a member of the brotherhood.