Why not? Football is fast, violent, and exciting. While most American sports fans *watch* football, not nearly as many *play* football, because you need at least a dozen or so people and a fairly open area to play it (unless you count the fun but highly dangerous hallway-football games we played in college.) Many more people play Basketball, because you only need two people (or one, if you're really desperate) and available basketball courts are a lot more commen than empty fields big enough for football.
Baseball and American football are two good examples of American sports
American sports
football, baskettball, and American football
American football and baseball. Americans of course also do well in many other sports, but those are not seen as 'typically American' in the way that these two are.
Football, Baseball, Basketball,
football,baseball soccer was not importin to the Americans
Soccer and Football
Americans did and still enjoy many spectator sports. Several include baseball, American football, ice hockey, golf and basketball.
football, american football and tennis + basketball
American Football
Football (Soccer to Americans) and Rugby
Baseball, basketball and football are not the main sports in Australia so I don't really think you can compare us. But aussies are good at all sports, it runs in the blood.