Clapper was the first NHL player to play twenty seasons, and one of only two to be an All-Star at both forward and defence. The right wing on the powerful "Dynamite Line"—one of the first forward lines to receive a nickname in hockey history—along with linemates Cooney Weiland and Dutch Gainor, he contributed to the breaking of several scoring records in the 1930s. Towards the end of his career, he was named player-coach of the Bruins, and held the coaching position after his retirement as a player.