Fat Part of the Bat (1910)

“Hunter, the second man to bat in that inning, caught one squarely on the fat part of his bat.” Scranton Truth, September 24, 1910, p10

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1918. “Ping Bodie…caught the ball with the fat part of his bat, lining it to right field” (Burt Whitman, Boston Herald and Journal, Apr. 21; Peter Morris).