part-time player (1924)

“He [Ownie Bush] left the [Indianapolis] Indians at the close of the 1908 season as one of the most brilliant shortstops ever developed, and returns to the Tribe as manager and part-time player.” “Indianapolis Is Ready for Play,” Muncie (IN) Star, April 15, 1924, p10

“After taking his diploma from Notre Dame in 1912, Frederick [“Cy” Williams] joined the Cubs and for three seasons was a part-time player, breaking into the box score only when right-handers were toiling against him.” “Veteran Cy Williams First of Phils to Round Into Form,” Wichita Falls Record News, March 29, 1925, p12. (Earliest example referring to just a player, rather than a player-manager.)

No earliest use given in 2009 Dickson Baseball Dictionary