The Seitz decision was a ruling by arbitrator Peter Seitz (May 17, 1905-October 17, 1983)  on December 23, 1975, which declared that Major League Baseball (MLB) players became free agents upon playing one year for their team without a contract, effectively nullifying baseball's reserve clause. The ruling was issued in regard to pitchers Andy Messersmith and Dave McNally.
Since the 1880s, baseball owners had included a paragraph described as the reserve clause in every player contract. The paragraph as written allowed teams to renew a contract for a period of one year following the end of a signed contract. Owners asserted and players assumed that contract language effectively meant that a player could be "reserved," by a ballclub's unilateral contract renewal, year after year in perpetuity by the team that had signed the player. That eliminated all market competition and kept salaries relatively low.
In 1975, Messersmith of the Los Angeles Dodgers and McNally of the Montreal Expos had had their 1974 contracts automatically renewed by their teams on the basis of this reserve clause. Since neither signed a contract during that option year, both insisted that they were free to sign with other teams the following season. The owners disagreed, arguing that under the reserve clause the one-year contracts were perpetually renewed.
The Major League Baseball Players Association (MLBPA) filed notices of grievance on behalf of both players on October 7, 1975. Eventually hearings were held on November 21, 24 and December 1, 1975 before an Arbitration Panel composed of MLB Player Relations Committee chief negotiator John Gaherin, MLBPA Executive Director Marvin Miller and Seitz, the Chairman and Impartial Arbitrator agreed upon by both opposing parties. Seitz ruled in favor of Messersmith and McNally on December 23, 1975, declaring:
The grievances of Messersmith and McNally are sustained. There is no contractual bond between these players and the Los Angeles and the Montreal clubs, respectively. Absent such a contract, their clubs had no right or power, under the Basic Agreement, the Uniform Player Contract or the Major League Rules to reserve their services for their exclusive use for any period beyond the renewal year in the contracts which these players had heretofore signed with their clubs.
Seitz's Opinion further stated:
The leagues involved in these proceedings, without delay, shall take such steps as may be necessary to inform and instruct their member clubs that the provisions of Major League Rules 4-A(a) and 3(g) do not inhibit, prohibit or prevent such clubs from negotiating or dealing with respect to employment with the grievants in this case; also, that Messersmith shall be removed from the reserve list of the Los Angeles Club and McNally from the reserve or disqualified lists of the Montreal Club.
In essence, the players were free to bargain with other teams because organized baseball could maintain a player's services for only one year after expiration of the previous contract. According to Gaherin, Seitz indicated soon after he heard arguments from both sides that he was leaning toward ruling for the players.
MLB appealed the decision to the United States district court for Western Missouri, but Seitz's ruling was upheld on February 3, 1976 by Judge John Watkins Oliver, and later by the 8th Circuit Court of Appeals. After all appeals were exhausted, Major League Baseball and the Major League Baseball Players Association signed a new agreement in 1976 allowing players with six years experience to become free agents.
- Bosman ruling, a 1995 European Court of Justice decision that outlawed a similar reserve system in European football (soccer).
- Eastham v Newcastle United, 1963 court case in England
- Curt Flood
- Free agent
- Marvin Miller
- Kansas City Royals Baseball Corp. v. Major League Baseball Players Ass'n, 409 F. Supp. 233, 261 (W.D. Mo. 1976) aff'd, 532 F.2d 615 (8th Cir. 1976) – Leagle, Inc.
- Chass, Murray (2000-12-23). "Baseball's Transfer Of Power". The New York Times.