The American Hockey League (AHL) is a professional ice hockey league based in the United States and Canada that serves as the primary developmental league for the National Hockey League (NHL). Since the 2010–11 season, every team in the league has an affiliation agreement with one NHL team. When NHL teams do not have an AHL affiliate, players are assigned to AHL teams affiliated with other NHL teams. Twenty-six AHL teams are located in the United States and the remaining five are in Canada. The league offices are located in Springfield, Massachusetts, and its current president is Scott Howson. In general, a player must be at least 18 years of age to play in the AHL or not currently be beholden to a junior ice hockey team. The league limits the number of experienced professional players on a team's active roster during any given game; only five skaters can have accumulated four full seasons of play or more at the professional level (goaltenders are exempt from this rule and can stay in the AHL indefinitely without being subject to this cap). The AHL allows for practice squad contracts. The annual playoff champion is awarded the Calder Cup, named for Frank Calder, the first President (1917–1943) of the NHL. The most recent champions are the Charlotte Checkers in 2019 as the Calder Cup playoffs were not held in 2020 or 2021.