The Liga ACB, known as Liga Endesa for sponsorship reasons, is the top professional basketball division of the Spanish basketball league system. Administrated by the Asociación de Clubs de Baloncesto (ACB), Liga ACB is contested by 18 teams, with the two lowest-placed teams relegated to the LEB Oro and replaced by the top team in that division plus the winner of the promotion playoffs. The competition was founded as the ACB Primera División on 1983 following the decision of clubs in the Liga Nacional, founded in 1957, to break away from the Spanish Basketball Federation and professionalize the league. The league's accumulated revenues were worth around €30 million in 2020, with Endesa and Movistar Plus+ contributing 50% of the revenues of the league. The league is a corporation where president Antonio Martín is responsible for its management, whilst the member clubs act as shareholders. Clubs were apportioned central payment revenues of €12 million in 2019–20. A total of 49 teams have competed in Liga ACB since its inception in 1983. Seven teams have been crowned champions, with FC Barcelona winning the title a record 16 times and Real Madrid 14 times, though Liga ACB also saw other champions, including Baskonia, Joventut Badalona, Bàsquet Manresa, Baloncesto Málaga and Valencia Basket. Liga ACB is one of the most popular professional indoor sports leagues in the world, with an average attendance of 6,236 for league matches in the 2018–19 season. This is the ninth-highest of any domestic professional indoor sports league in the world and the fourth-highest of any professional basketball league in the world, behind the National Basketball Association, the EuroLeague, and the Women's National Basketball Association. Competition format The competition format follows the usual double round-robin format. During the course of a season, which lasts from October to May, each club plays every other club twice, once at home and once away, for a total of 34 games. Teams are ranked by total wins, with the eight highest-ranked clubs at the end of the season plays the playoffs and the winner of the playoffs is crowned champion. Relegation and promotion A system of relegation and promotion exists between the Liga ACB and the LEB Oro. The two lowest placed teams in Liga ACB are relegated to the LEB Oro, and the top team from the LEB Oro promoted to Liga ACB, with an additional club promoted after a series of playoffs