Guttman, Allen [1993]. «The Diffusion of Sports and the Problem of Cultural Imperialism». A: Eric Dunning, Joseph A. Maguire, Robert E. Pearton. The Sports Process: A Comparative and Developmental Approach. Champaign: Human Kinetics, p129. ISBN 0880116242 [Consulta: 26 gener 2008]. «the game is complex enough not to be invented independently by many preliterate cultures and yet simple enough to become the world's most popular team sport»
Frederick O. Mueller, Robert C. Cantu, Steven P. Van Camp [1996]. «Team Sports». A: Catastrophic Injuries in High School and College Sports. Champaign: Human Kinetics, p57. ISBN 0873226747 [Consulta: 26 gener 2008]. «Soccer is the most popular sport in the world, and its popularity is growing in the United States. It has been estimated that there were 22 million soccer players in the world in the early 1980s, and that number is increasing. In the United States soccer is now a major sport at both the high school and college levels»
