Sport fans seem to forget that sport is all about playing and having fun. It seems they think "I've grown up loving this football team, so the label is part of my personality".
Sometimes I believe some people care more about sport results, than they care about their relatives.
Maybe it's in our genes, to love the place where we come from (like the Salmon does). Since there aren't much small places and villages any longer, maybe people stick all their lives to some football or hockey team instead.