Broadly speaking, European sports evolved before the spectator-sports industry and, as a result, are primarily for playing; American sports evolved afterwards and have been shaped (to a greater extent) by needing to be good to watch.
That's the formal codification of football - Association Football, Rugby Football (both League and Union). The games themselves have been around for hundreds of years.
American football is an enigma to foreigners in the same way that cricket is an enigma to Americans. It's just horribly complicated and weird and there's no way to get a handle on it if you weren't raised with it IMO. (Historically, gridiron is just another rugby variant, except with added down-and-distance rules, forward passes, and blocking. I like the Canadian rules a little better than the American rules, but the best players and teams are American so that's what most people watch.)
Basketball and baseball, however, are tremendously popular around the world.
I was also thinking about NASCAR. What could compel people to watch a bunch of cars drive around and around in a circle is beyond me. I enjoy motor sports, but unlike WRC, F1, AMA road racing, STCC or any other type of racing, NASCAR is like watching someone hula hoop for an hour.
