When assessing the “dirty” aspect of a basketball play, a good but non-all-encompassing question to ask is “if I did this in a pickup game, would someone fight me”. The play in question one hundred percent qualifies, not because it’s so physically egregious (it’s not), but because it’s such an obvious cheap shot (the ball isn’t even in bounds!) that it’s clear the aggressor wanted everyone to know it was a cheap shot. 

This is not “I am a tougher basketball player than you”, this is “I can do whatever I want to you”. And look, I get that a lot of people are horrified by the Matt Barnes-es of the world imploring for some extra-legal, on-court revenge justice. I’m usually not into that stuff either, to be honest. But that’s only when the powers that be are making a real effort to regulate what’s happening to people on the court. If somebody goes after one of my best players, after the play, the league needs to throw him or her out of the game, period. Otherwise, the 12th man is coming out and putting the aggressor into the basket stanchion on the next play, and the league can sort all that out instead.