“…when Stratton was in the box, he was given the ‘corners’ of the plate in every instance, while Ramsey was made to split the plate or a ball was called.” Joe Pritchard, Sporting Life, September 20, 1890 p. 8 [Richard Hershberger]
NOTE: But see “outside corner” (first use 1886) “inside corner” (first use 1888) (Ken Liss)
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1901 (Burt L. Standish, Frank Merriwell’s School Days, p. 242; Edward J. Nichols).