Curveballer (1910)

“There is a possibility, too, that the veteran pitcher, Vic Willis, of the world’s champions, will be secured by purchase … Griff made no haste in the matter, which he still has under consideration, and he may decide to buy hte big curve-baller.” Jack Ryder, “Vic Willis May Be Purchased by Reds from Pittsburg” (subhead), Cincinnati Enquirer, February 1, 1910, p6
— Also appeared in Pittsburg Press

No earliest use given in 2009 Dickson Baseball Dictionary