American football
The main leagues that play American football are the professional National Football League (NFL), and the National Collegiate Athletic Association (NCAA), which plays college football.  In the National Football League, players can be paid millions of dollars.  In the National Collegiate Athletic Association, players simply play for the pride of their school, scholarships, or for the chance to join a national team.  Over a million boys (and a number of girls) play high school football. There is also a closely related sport called Canadian football (CFL).