Masterton graduated from Denver with an engineering degree, but decided to turn pro. He signed a contract with the Montreal Canadiens in 1961. He was assigned to the Hull-Ottawa Canadiens of the Eastern Professional Hockey League. In 1962, he was promoted to the Cleveland Barons of the AHL, where he led the team with 82 points.
After he failed to make the Canadiens roster in 1962, he decided to complete his master's degree at the University of Denver. He accepted a job at Honeywell in Minneapolis. After taking a year off from hockey, he regained his amateur status and played two seasons for the St. Paul Steers of the United States Hockey League. After becoming an American citizen, he joined the US National Team in 1966, where he served as the team's captain.
When the NFL expanded from six teams to twelve in 1967, Masterton had another chance to play pro hockey. One of the six new teams introduced to the league set up in Bloomington...the Minnesota North Stars. Masterton was the first player signed by coach and GM Wren Blair. As a 29 year old NHL rookie, Masterton debuted against another new NHL team: the St. Louis Blues. It was in that game, October 11 1967, that Masterton scored the first goal in Minnesota North Star history in a 2-2 tie with the Blues.
"It sounded like a baseball bat hitting a ball." - North Stars teammate Andre BoudriasMasterton was playing in his 38th career NHL game against the California Seals at the Met Center on January 13th 1968 when tragedy struck. While carrying the puck across the blue line, he was checked by Seals defensemen Larry Cahan and Ron Harris. One of their sticks got tangled in Masteron's skate and the other defender hit him with a clean check that knocked him backwards. The impact of the hit caused Masterton to lose consciousness before hitting the back of his head on the ice.
He was rushed to Fairview Southdale hospital, where doctors determined the swelling in his brain was so severe that they couldn't operate. 30 hours after the hit, his family decided to remove him from life support and passed away on January 15th 1968. He is the only NHL player to die from an injury suffered during a game.
At the time, helmets were required in NCAA hockey, but not in the NHL. Masterton was not wearing a helmet when he fell. Only a handful of NHL players were wearing helmets at the time. It would take eleven years for the NHL to make helmets mandatory to incoming NHL players...players who had signed pro contracts prior to June 1 1979 were given the option not to wear a helmet. It wasn't until Craig MacTavish retired following the 1996-97 NHL season that every player in the league was wearing a helmet.