Unconditional Release (1887)

George McGinnis will be released by the Cincinnati management. There was no effort made to sell him by President Stern, as an unconditional release will give him a much better opportunity to secure a desirable position.St. Louis Post-Dispatch, June 20, 1887, p8

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1893. “Bob Caruthers, the well-known ball player, has been given his unconditional release by President [Chris] Von der Ahe, and is free to sign where he pleases” (Atlanta Constitution, March 17; Peter Morris)