Outside Corner (1886)

“The pitcher’s out-curve will not fool so many players this year, as the batter stands almost on the home plate. A ball that comes out of his reach must go fully a foot from the outside corner of the home plate.” The Macon Telegraph, April 15, 1886, p5

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1901 (Burt L. Standish, Frank Merriwell’s Marvel, p. 206; Edward J. Nichols).