Fifty years ago, Minnesota North Stars player Bill Masterton became the first, and to-date only, NHL player to die as a result of an in-play injury. He died two days after being checked during play against the Oakland Seals, aged 29.
It was his death that opened the debate on making the wearing of helmets compulsory. The Bill Masterton Memorial Trophy is presented each year in his memory.
A short film about him and the incident.