yellow hammer

Etymology
The origin is.

Noun

 * 1)  A curve ball, especially a breaking curve that is particularly difficult to hit.
 * 2) * 2004, Michael Coffey, 27 Men Out: Baseball's Perfect Games, updated edition, page 106
 * Williams, getting steady doses of Koufax's "yellow hammer," struck out looking at a curve, Sandy's fifth K.
 * Williams, getting steady doses of Koufax's "yellow hammer," struck out looking at a curve, Sandy's fifth K.