Why ??

Because the mother of the idiots is always pregnant MYRY

Soccer is a game of courage and vigorous physical activities. So some one interested in soccer must be a fan of vigorous physical activities.

I think as soccer is involves lots of phisycal activity and strength and energy, the players become excited while playing. In the game kicking or guarding players are a very common fact. So the supportes of this game also feel very excited and sometimes become violent in the game.

Its the passion of the game, but seriously, some people take it too seriously. I used to know an English family and they said that football's more important than life. but i think its just a certain large group of fans in general that become violent and noticed - so they don't represent all football fans.