Bill Masterton is the only man to die of injuries sustained in a National Hockey League (NHL) game. He remains the last fatality in any professional team sport involving a direct in-game injury in North America. While Masterton was originally thought to have suffered a fatal brain injury while being checked on the ice, later analysis of the case revealed evidence of second-impact syndrome and the effects of prior concussions. Masterton's death sparked both an immediate debate in the NHL on whether helmets should be compulsory and the NHL's first vote on mandatory helmet use. Although the subject of mandated helmet use met with resistance in the 10 years after Masterton's death, especially from hockey owners and coaches, the NHL finally legislated helmet use by all players entering the league beginning in the 1979–1980 season.
Several awards, including one recognizing the NHL player who best exemplifies the qualities of perseverance, sportsmanship, and dedication to hockey, have been created in memory of Masterton. However, his legacy extends far beyond the awards that bear his name. His death was the seminal event bringing head safety to the forefront of a game that was both unready and unwilling to accept change. An increase in mainstream media attention in recent years has led to unprecedented public awareness of brain injury and concussion in hockey and other sports. Advances in the diagnosis and treatment of head injury in sports have occurred recently, the impetus for which started over 45 years ago, when Bill Masterton died.