The incident occurred during the third period of Tuesday’s Game 3 between the Penguins and Rangers.
Pressured along the end boards, Letang played the puck, looked up and then followed through with his stick, whacking Stalberg right around the chin. There was no call on the play, but television cameras caught the incident and ran a slow-motion replay of the slash.
The Penguins grabbed a 2-1 series lead with a 3-1 victory at Madison Square Garden. Letang scored into the empty net to put Pittsburgh up by two goals in the final seconds of the third period.