Foul Off (v.) (1888)

“With four balls and two strikes, Keefe put a number of good balls over the plate, all of which Hines met and fouled off, until at last Keefe threw a wide one and the batter took his base.” “Giants Fun with Healy,” Indianapolis Journal, May 10, 1888, p3

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1893.  “The proposed amendment, by which the unskilled will be charged with a strike for ‘fouling off’ whether through itntention or inexpertness.” (The Sporting News, Dec. 23; Peter Morris)