San Francisco Giants manager Roger Craig: In his first full year as Giants' manager, Craig made "Hum Baby" the baseball phrase of 1986. A player he liked was a "hum baby," a good play was a "hum baby of a play", one could merely exhort "hum baby" from the dugout in lieu of a "let's go". . . the potential uses were infinite.
by Giants fan October 19, 2012
Baseball chatter in which the infielders encourage the pitcher to fire off a fast ball, so fast that it hums. It was in widespread use in 1960s Little League (I know from experience) and probably predates that, so the Roger Craig origin in the mid 80's that several people have reported is simply incorrect.
by fireballxl5 July 20, 2014