Hockey's unwritten code is a time honoured tradition and had been around since the beginning of the game. Players use the code as a way to police themselves when they're on the ice, if the code gets broken, it more often than not results in a form of retribution. Every player knows and understands the code, but that doesn't stop some players from crossing the line.
During a preseason game between the Sault Ste. Marie Greyhounds and Sudbury Wolves, things popped off during a stoppage of play when the code was broken by Wolves forward Landon McCallum. The video shows McCallum appearing to tear off a chain they is around Alex Kostov's neck.