goalkeeper due to injuries or suspensions. The pool goalkeeper trains with an MLS club or an affiliated team when not assigned to a team; some pool goalkeepers, including Tim Melia, have gone on to be signed to permanent contract with their assigned teams. In the past, when rosters were smaller, there were multiple goalkeepers signed to the pool, however, in recent years only one or two keepers are signed as team rosters are much larger. Designated Players and allocation money MLS has also introduced various initiatives and rules intended to improve quality of players while still maintaining the salary cap. Rules concerning Designated Players and allocation money allow for additional wage spending that is exempt from the salary cap. These initiatives have brought about an increase in on-field competition. The designated player (DP) rule allows teams to sign a limited number of players whose salary exceeds the maximum cap; in 2017, each DP player only counted as $480,625 (the maximum non-DP salary) against the cap. Instituted in 2007, England's David Beckham was the first signing under the DP rule. The DP rule has led to large income inequality in MLS with top DPs earning as much as 180 times more than a player earning the league minimum. In the 2013 season, 21% of the league's wage spending went to just five players; this stretched to 29% on the top 6 players in the 2014 season. The league's "Core Players" initiative allows teams to re-sign players using retention funds that do not count against the salary cap. Retention funds were implemented in 2013 as a mechanism for MLS to retain key players; among the first high-profile players re-signed using retention funds were U.S. national team regulars Graham Zusi and Matt Besler. MLS teams can also obtain allocation money, which is money that the team can use on player salaries that does not count against the cap, and teams can earn allocation money in several ways, such as from the transfer fees earned by selling players to teams in other leagues. MLS teams can also use Targeted Allocation Money (often referred to as TAM), an initiative announced in 2015. Teams can use TAM funds to attract high-profile players by "buying down" contracts of players to below the Designated Player level. High-profile players for which TAM funds were used include Hector Villalba, Zlatan Ibrahimović and Giorgio Chiellini. Youth development MLS has introduced various