In the first period, Toronto Maple Leafs third line centre (who is a first line centre on half the teams in the NHL) Nazem Kadri was hit hard and suffered a concussion.
He returned to the game briefly, but then left for good and did not come back.
Hopefully he is fine, because a long term loss of Kadri would be a catastrophic disaster for the Toronto Maple Leafs.
Nazem Kadri
Kadri was one of just eight centres in the NHL to score over 30 goals in the last two years (Auston Matthews and John Tavares also make the list) and he is intrinsic to the Leafs success.