There is an excellent treatment of fighting in hockey in:
"The Code: The Unwritten Rules of Fighting and Retaliation in the NHL" by Ross Bernstein (2006)
I recommend reading this book if you have any interest the role of fighting in the NHL. I can't really point you to a specific part of the book off the top of my head, but in general, hockey fights are sort of a check on unchecked aggression against the more high profile (and potentially smaller) players in the game. Generally, if a player decides to beat up on a superstar / finesse player, they will have to deal with the "Enforcer". The enforcer is usually the big man on the team. Occasionally, not even that good of a player... just a bruiser, and a deterrent to trying to play dirty against the guys less able to defend themselves.
The dynamics of how this plays out on the ice are the topic of this book, and there's been many articles written about it as well. In recent years, this culture within hockey is starting to be condemned. Especially after the death of Derek Boogaard who died from drug complications brought on by the many concussions he received during fights filling his role as an enforcer in the NHL. This documentary by the New York Times has received a lot of attention and is starting to change attitudes about whether the game can get along without fighting.
http://www.nytimes.com/video/sports/100000002879034/punched-out-the-death-of-derek-boogaard.html
Fighting isn't allowed in hockey; those who do fight are penalised. However unlike other sports it does not lead to expulsion from the game (I speak in terms of the NHL and other main North American leagues; in Europe, international competitions, and US universities, this is not true). There are different ideas regarding why hockey is more lax on fighting, and Bernstein's book does cover a lot of them. My opinion on it (in part influence by the article "Talk About Strenuous Hockey": Violence, Manhood, and the 1907 Ottawa Silver Seven-Montreal Wanderer Rivalry by Stacy L. Lorenz and Geraint B. Osborne, Journal of Canadian Studies 4:1 (2006): 125-156) is that hockey has long been a vehicle for participants to express their physicality in a means otherwise not available to them. This was especially true in the early days of the sport, where Victorian ideals meant that men had to be more reserved and proper, especially the more wealthy folks who first engaged in organised sports. Thus hockey provided an outlet of near-unreserved aggression and physicality, and fighting was thus permitted to serve such a purpose. It has become ingrained into the sport now, and while it's likely to eventually be removed, this has faced opposition because of the historical legacy.