By the time of the incident, the game was out of reach for Montreal as the Penguins led 6-3. Subban, never afraid to get under someone's skin, decided to take out his frustration on Morrow. That turned out to be a poor decision.
Notice how Subban completely whiffed on his first punch.
Morrow started yapping at Subban, challenging him to another fight once they got back on the ice. Subban challenged him to a noogie contest.