Just like hockey, teams would bring on a guy just to beat the ---steaming pile of meadow muffin--- out of a key player on the other team.
Rarely (if ever) do the true fighters in hockey go after the other teams key players. You're not gonna see Georges Laraque just start pummeling Jason Spezza, your gonna see him square off against Chris Neil.
That's pretty much the reason that teams have fighters, to keep the skilled players safe. If you take a cheap shot at Crosby or Hossa, you know you're gonna have to deal with Laraque later in the game.
On the other hand there are plenty of dirty players in the league (Chris Simon) who will intentionally try to hurt someone.
There is a huge difference between the fighters that will fight the other teams goons and flat out dirty players that try to injure.
Now, all that being said, the content of that video is disgusting. Patrick Roy should be banned for life for encouraging his son (or any player) to act that way.