It is a well-known fact that fans of 2 different clubs don’t get along very well with each other. A Manchester United fan will never see eye to eye with a Liverpool fan or a Manchester City fan. A Borussia Dortmund fan has a sworn enmity with German clubs Schalke and Bayern Munich.
Often, this rivalry has its roots in how the clubs were founded, and whether the fans of the clubs in question are from certain demographics which don’t mesh well with each other in general. For example, the Internazionale-Milan rivalry was based on the fact that most Inter fans were well-off, affluent and the club was gladly accepted international players into its squads, whereas the Milan fanbase was dominated by the people of Milan, and only fielded Italian players.
Today, however, the antagonism between fans of different clubs could be kindled by a variety of different reasons other than demographics, because of the international reach of the contemporary game. Fans in Asia, Africa and the Americas have been known to get physically violent in altercations with fans of rival clubs: mostly European clubs. The following 5 are some of the reasons for this enmity:
#1 The grass is always greener on the other side
Unless you are a fan of Manchester United, Bayern Munich, Real Madrid or Barcelona (The Big 4 clubs of world football), you are supporting a club whose scale of success is not as big as these 4. Even if you are a fan of any of these 4 clubs, there is always something missing from your club that others can use to take the mickey out of the club you support - which is not quite palatable for you, as a fan.
A typical example of this sort is the situation that Real and Barca fans find themselves in, after this past season. While Barca fans gleefully point to their domestic double, Real fans can hold up the Champions League trophy, which is the biggest prize of them all. And yet, neither of them can quite claim to be genuinely better off than the other.
Because the grass is always greener on the other side, the herd on this side of the fence shall always be jealous of and angry with the rest of the herd.