The Collaborative International Dictionary of English v.0.48:

change-of-pace \change-of-pace\ n. (Baseball)
   a baseball pitch thrown with little velocity when the batter
   is expecting a fastball; -- called also change-up.

   Syn: change-up, change-of-pace ball, off-speed pitch.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

change-up \change-up\ n. (Baseball)
   same as change-of-pace.

   Syn: change-of-pace, change-of-pace ball, off-speed pitch.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

change-up
    n 1: a baseball thrown with little velocity when the batter is
         expecting a fastball [syn: change-up, change-of-pace,
         change-of-pace ball, off-speed pitch]