He's a hothead, but Goodwin is the one who escalated that situation.
Why what happened?
Morris has been asked to be a leader by Phoenix's new coach.
So, Goodwin starts the game against the Warriors terribly. Mental mistakes, bad effort. Goodwin is on the bench. Markieff comes up to him, barking. We don't know if he was blaming Goodwin, trying to coach him, or trying to get him fired up.
Regardless, Goodwin didn't take it well. They seem to slap at each other's hands (the camera is blocked here) and then Goodwin gets up and lashes out at Markieff aggressively. Markieff seems calm when teammates intervene; Goodwin keeps going at him.