“Texas Leaguer Defined: Harris’ men got but six hits off Harper, and half of these were what is known to the profession as Texas leaguers, but why so called is beyond the ken of mortal man. If a batted ball drops between the in and out field in such a way that neither can get it they call the hit a Texas leaguer, which is perhaps as good a name as any.” San Francisco Examiner, April 8, 1892, p7
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1892. “Then Peter Nabb came to the fore with one of his little three-baggers, a regular Texas Leaguer, which landed fair just beyond first and then bounded and rolled away in under the bleachers” (Los Angeles Times, Dec. 16; Benjamin Zimmer).