All of you arguing Ariza's intentions need to go and read the rulebook. It's not a factor. It's not even mentioned. The criterion for a flagrant 2 is "unnecessary and excessive contact". It's the act that's punished, not the intent. And that's the way it should be. How can a referee or league official possibly determine intent? They can't read minds, and no player, knowing he's facing a suspension, is going to admit he was trying to hurt another player.
So, regardless of intent, Ariza's actions were "unecessary and excessive". They were also reckless and put another player, in a very vulnerable position, at risk of serious injury. Punish the action, not the intent. Send a message that taking down a player, who has left his feet, from behind with a blow to the head, is NEVER allowed.
Unfortunately, the NBA botched this big time by not suspending Ariza for a game for his dangerous actions.
BNM