League system
A league system is a hierarchy of leagues in a sport, usually with a system of promotion and relegation, between consecutive levels of the hierarchy. They are often called pyramids, due to their tendency to split into an increasing number of regional divisions, the further down the pyramid one descends. League systems are used in a number of sports, especially association football, rugby league, and rugby union.
In North America, a similar league system exists, but without promotion or relegation. Most professional sports are divided into major and minor leagues. While baseball and association football (known as soccer in North America) have well-defined pyramid shapes to their minor league hierarchies, ice hockey's professional minor league system is linear, with one league at most of the four levels of the game. Basketball follows a roughly inverted-T-shaped three-level system.
Gridiron football does not operate on a league system, in part because of that sport's reliance on amateur college football for development of future players (other North American sports also recruit players from colleges and universities, but it is far more pervasive in professional football), and in part because the expense and injury risk of the game makes maintaining a minor football league impractical. The indoor American football system can be seen as an informal league system, but there are widespread differences between the indoor and outdoor forms of the game.
