Line Drive (1876)

“Hines, for instance, hit three long line drives just where some one was waiting for him, and Anson, McVey, and White were similarly unlucky in having what seemed safe line hits fly right at a fielder.” Chicago Tribune, May 26, 1876, p8

Earlier example from cricket:

“…. and then Hargreaves put out a hot line drive that went under the ropes and, by the rules, gave four runs.” Philadelphia Inquirer, September 14, 1875, p3

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1888. “Sam Thompson made a running catch of [Cap] Anson’s vicious line drive” (Detroit Free Press, May 27).