Since the introduction of league football, most club sides play a number of friendlies before the start of each season (called pre-season friendlies). Friendly football matches are considered to be non-competitive and are only used to "warm up" players for a new season/competitive match. There is generally nothing competitive at stake and some rules may be changed or experimented with (such as unlimited substitutions, which allow teams to play younger, less experienced, players, and no cards). Although most friendlies are simply one-off matches arranged by the clubs themselves, in which a certain amount is paid by the challenger club to the incumbent club, some teams do compete in short tournaments, such as the Emirates Cup, Teresa Herrera Trophy and the Amsterdam Tournament. Although these events may involve sponsorship deals and the awarding of a trophy and may even be broadcast on television, there is little prestige attached to them.