It's a well-known fact that fighting is a commonplace in hockey, but there are still unwritten rules that apply. Rules that guard against disgraceful moments like the one seen in the Boston/Penguins game.
Tensions were already high according to CBS' Eye on Hockey, but things reached a boiling point when the Penguins' James Neal kneed an already floored Brad Marchand, who looked injured afterward.
That was an incredibly unsportsmanlike act by itself, but it doesn't compare to what happens afterward. In the scrum immediately following the incident, the Bruins' Shawn Thornton attacked Brooks Orpik from behind by pulling him down to the ice and pummeling him. The action left Orpik unconscious and on his way out of the rink in a stretcher. It was in all an unsightly act that has no place in sports.
Marchand stayed in the game.
[via Eye on Hockey]