It really wasn't called by the term "change-up" until at least the 1950s. Before that, it was likely known as an off-speed or "slow-ball" pitch. It was also known as a veteran's pitch. One used by guys trying to hang on in the majors that were losing their fast-ball. It didn't become devastating until the late '80s to early '90s, when Leo Mazzone started to teach it to guys. Maddux, Glavine, Smoltz and the successful Atlanta Braves pitching staff made it popular. Santana, Hoffman, Gagne and others - made it a standard pitch. A well-located 89-92 mph fastball and a devastating change-up are the two deadliest things in a pitcher's arsenal. Forget heat - If you have location and accuracy, that batter is dead to rights.