“That bane of young hitters, the curveball, is called the hook, deuce or No. 2, drop, rainbow, big yakker and the do drop in.” Bart Ripp, Albuquerque Journal, August 3, 1975, p43
Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1979. “Total command of the yakker” (Thomas Boswell, The Washington Post, May 21, 1979).
