changeup is a type of pitch in baseball. Other names include change-of-pace and simply change. The changeup is sometimes called an off-speed pitch, although that term can also be used simply to mean any pitch that is slower than a fastball.
The changeup is thrown with the same arm action as a fastball, but at a lower velocity due to the pitcher holding the ball in a special grip. In his book "Pitching like a Pro: A Guide for Young Pitchers and Their Coaches, Little League through High School," Leo Mazzone makes an analogy stating that when a pitcher throws his best fastball, he puts more in it; the changeup is such that one throws something other than his best fastball. By having this mindset, the pitch will have less velocity on it in addition to the change in grips. This difference from what is expected by the arm action and the velocity can confuse the batter into swinging the bat far too early and thus receiving a strike, or not swinging at all. Should a batter be fooled timing wise on the pitch, and still make contact, the batter will be early, causing foul balls and/or putting the ball into play, usually resulting in an out, so long as the batter was fooled significantly. In addition to the unexpectedly slow velocity, the changeup can also possess a significant amount of movement, which can bewilder the batter even further. The very best changeups utilize both deception and movement. Ron Darling recently described Johan Santana as having one of the most effective changeups in Major League Baseball, due in part to the difference in speed between their fastballs and changeups. Trevor Hoffman and Jamie Moyer are also known for having very deceptive changeups, even though their pitching velocities are very different (Moyer 76, Hoffman 90). Philadelphia Phillies up-and-coming star Cole Hamels has a devastating low-80's change-up that complements his low-to-mid 90's fastball, and has already developed as his out-pitch and one of the best change-ups in baseball.
As pitchers age, some learn to greatly extend their careers after losing speed on their fastballs by taking advantage of the differences in speed between an effective changeup and a fastball of any speed. One such pitcher is Trevor Hoffman, who is renowned for a devastating changeup combined with an average speed fastball.
There are several types of changeup, which are generated by using different grips on the ball during the pitch.
The most common type is the straight change. The ball is held with three fingers (instead of the usual two) and closer to the palm, to kill some of the speed generated by the wrist and fingers. This pitch generally breaks downward slightly, though its motion does not differ greatly from a two-seam fastball.
Another common grip is the circle changeup. The pitcher forms a circle with his index finger and thumb, using these two fingers to grip the seams of the baseball. By pronating the wrist upon release, this pitch tends to break slightly in the same direction as a screwball. More or less break will come about from the pitcher's arm slot, the more three-quarters or side-arm angle, the more break generally. Pedro Martínez has used this pitch throughout his career to great effect, and many consider it to be his best pitch. Before shoulder injuries made him lose velocity, Martinez countered his 96-98 mile per hour fastball with this devastating 80-82 mile per hour screwball-like changeup. Tom Glavine's changeup grip is a circle change grip, but because he does not pronate his wrist, he doesn't have the screwball movement, but rather, more sink on the pitch than the straight change. 2 time Cy Young Award winner Johan Santana has arguably the best circle change in baseball, and many cite it as his most effective pitch. Boston Red Sox set-up man Eric Gagné also has a highly effective changeup pitch, which he throws at around 70 miles per hour. However, the effectiveness of Gagné's change was greater as a member of the Los Angeles Dodgers because his fastball reached velocities approaching 100 M.P.H. and his change as low as 67 M.P.H.