I'm going to side with Mario on this one. He's trying to unhook his arm from the pick setter (who's grabbing his arm) and he unintentionally hits Dirk with it. Dirk knew it too otherwise he would have been a lot angrier.
I can see where he was coming from about freeing up his arm, but I'm assuming the suspension was due to this being the 2nd time this has happened in a very short period of time. He drilled Blake Griffin in the neck area too.
The camera angle from above looks like like he slipped or was being pulled down. The elbow that flailed up doesn't look intentional.
1 game suspension seem ridiculous. Clearly he deserves at least 1 week in jail. The Mavs player was clearly trying to hold Chalmers back in his attempt to punch Dirk, but Chalmers broke free anyway and punched dirk.
Difficult call since players always try to make extra contact when fighting through picks. Also wonder if there were any previous plays of frustration and jostling that led up to it. On the flip side, or directly related sequentially, it seems like he immediately knew he shouldn't have had his arm hitting Dirk's head and was trying to take it back and proclaim innocence. I think he had to have been somewhat reckless/careless as someone else mentioned to throw it out like that, even if it was being held or stuck before, which is why I think it's still partly intentional on his part to have it come out flailing and snap right into someone's face like that.. Usually it were out of frustration, you would do it more if you were down by 20, not up for 5 or 6.
Chalmers definitely has a fair argument. His arm was clearly held and he was trying to pull away from it. His reaction looks innocent. He'd also have to be an idiot to get an intentional flagrant with 5 minutes to go only up 5.