Don has summed it up perfectly!

This has nothing to do with "the spread of Americanism", it has to do with loutish young sports fans of the stupidest kind, too much beer, and too much adrenalin. It has happened before in Canada after Stanley Cup hockey games. There was the famous "Montreal Riot", for example, and I think there was one in Toronto once too. It happens just about anywhere now and then, wherever the young, the restless, the immature, and the not too bright gather to observe our culture's version of the Roman Games... ;-)

Here is a historical account of the famous 1955 hockey riot in Montreal, Canada.

The Richard Riot (in Montreal)