First Sacker (1899)

“Some satisfaction was gained by the faithful through Lave Cross finish first among the third baseman and O’Connor tying Dillon and Clark, the two Pirates, for supremacy among the first sackers.” “Comparison of How the Clubs Finished in 1898 and 1899,” St. Louis Globe-Democrat, October 29, 1899, Part 4, p4

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1905.  (Sporting Life, Oct. 2; Edward J. Nichols).