“For the first time this season, an Umpire—it was Mr. Cummings, of the Enterprise—performed his whole duty. He called both pitcher and striker closely to their business, calling balls and strikes promptly and at the same time keeping a keen eye to the field and bases.” Brooklyn Daily Eagle, June 19, 1866, p3
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1871. “The umpiring…was perfectly fair and impartial, although a leniency towards both pitchers and batsmen, in calling balls and strikes, lengthened the game.” The Cleveland Morning Herald, May 22, 1871.