College football refers to gridiron football played by teams of student athletes. It was through college football play that American football rules first gained popularity in the United States. Unlike most other sports in North America, no official minor league farm organizations exists in American or Canadian football. Therefore, college football is generally considered to be the second tier of American and Canadian football; one step ahead of high school competition, and one step below professional competition (the NFL). In some areas of the US, especially the South and the Midwest, college football is more popular than professional football, and for much of the 20th-century college football was seen as more prestigious. A player's performance in college football directly impacts his chances of playing professional football. The best collegiate players will typically declare for the professional draft after three to four years of collegiate competition, with the NFL holding its annual NFL draft every spring in which 256 players are selected annually. Those not selected can still attempt to land an NFL roster spot as an undrafted free agent.