There are probably a number of valid reasons both historical and contemporary for why football is presently so popular.

However I would like to highlight the fact that football unlike Tennis, Rugby, Cricket, Baseball, Basketball, American Football or AFL managed to transcend both social classes (outside the UK) and cultures.

The existence of football clubs might go some way to explaining this ability, since in many cities in the world, different group could start up their own club cheaply and compete. For example: the aristocracy would associate with one team and the working class another (as is the case with Sporting and Benfica Lisbon). The Glasgow derby remains heavily sectarian between the city's Catholic and Protestant supporters.

Another advantage is perhaps the simplicity of the game; it may be reduced to any numbers of individuals and still maintain its essence without the need for much equipment either.