Here's a link to a picture of Taylor Hall and his head wound as a result of a teammate's skate slicing his head during warm up before a game. This has sparked a huge debate whether NHL players should wear helmets during warm up. Before this, only the New York Rangers followed this belief, but after the incident the Toronto Maple Leafs have agreed to as well. I think that it was an isolated incident and not common at all. Although, with pucks flying everywhere and concussions becoming a large part of the news, all players should keep their helmets on for safety.