| Hughes, Ian 31 March 2008 | Under the system used in Argentina and most of Latin America, two season titles are awarded each year — the Apertura and Clausura |
|---|---|
| Catastrophic Injuries in High School and College Sports | Sport Matters: Sociological Studies of Sport, Violence and Civilisation |
Stormer, Neil 20 June 2006.
| Austin, Merrill 10 July 2007 | The number of competing teams has varied over the history of the competition |
|---|---|
| It has been estimated that there were 22 million soccer players in the world in the early 1980s, and that number is increasing | See Hill, Blake and Clark 1998 ; Schuster 1998 |
Ingle, Sean; Glendenning, Barry 9 October 2003.
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