Bonus rule
The bonus rule was a contractual rule affecting major league baseball intermittently between 1947 and 1964, meant to prevent teams from assigning certain players to farm teams. The rule stipulated that when a major-league team signed a player to a contract with a signing bonus above a certain threshold, the team was required to keep that player on their active roster. Any team that failed to comply with the rule lost the rights to that player's contract, and the player was then exposed to the waiver wire.
The rule was first instituted in 1947, removed in December 1950, and re-introduced in December 1952. As in force for the 1953 though 1957 seasons, a player subject to the rule had to be on the team's active roster for two full seasons, after which he could be assigned to a farm team without repercussions. The rule was again rescinded in 1958, but re-established for the 1962 major-league expansion, with different and more relaxed stipulations. It was finally abolished in 1965, when the Major League Baseball draft was initiated.