“As regards the pitching, ‘Walker’s battery’ proved to be very effective in aiding to achieve the result…” New York Sunday Mercury, July 10, 1864 [Richard Hershberger]
NOTE from Richard Hershberger: Walker was the pitcher for the Actives. I take the form “Walker’s battery” to be a riff off the military usage of the day of naming a unit by its commander, e.g. “Sykes’ Division.” Walker here is the commander of the battery, which consists of himself and Rooney, the catcher.
COMMENT from Ken Liss: There was a Walker’s Battery in action and in the news in June 1864. It is possible that the above use was a play on the name of that military unit.
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1868 (Chadwick Scrapbooks; Edward J. Nichols).
