“Chief Roseman was on the war path yesterday. He swung his war club viciously, and touched up our own Lawrence Barrett McKeon in a very lively manner.” The Cincinnati Enquirer, September 25, 1885, p2
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1913. “Bill [Leard] grabbed his trusty war club and approached the plate with the fixed idea of losing the ball over some one of the fences” (San Francisco Bulletin, May 17; Gerald L. Cohen).