To fend off possible future challenges to the legality of the standard contract and its reserve clause, new wording provides for compensation to the player for the right to renew. A player’s salary is specified as 75 percent for his services and 25 percent for the privilege of reserving them for the following season.

On July 7, 1912 To fend off possible future challenges to the legality of the standard contract and its reserve clause, new wording provides for compensation to the player for the right to renew. A player’s salary is specified as 75 percent for his services and 25 percent for the privilege of reserving them for the following season.

Source:
Baseball Reference July 7