I think the fact he's had 2 seasons in the last 3 years where he failed to play 50 games is more of a sign that his impact for GS isn't what it used to be. With guys like Moody, Looney, Poole, Wiggins, Porter Jr., Payton II, and Kuminga now on the squad and all under 30 seems like a changing of the guard.
The timing is bad, and it wasn't like they had a scuffle on the court and he threw a punch. From the clip shown he instigated everything, approaching Poole and then sucker punching him. Had this happened 3 or 4 years ago when Green was still playing all the time then maybe it'd be less of a deal. Mostly I think the fact Poole hadn't signed his extension is going to force GS into a tough situation.