Changeups (Off-Speed Pitches)
A pitch does not have to only change directions in order to deceive batters. Differing or slow velocities can also be used to make pitches harder to hit; these types of pitches are called off-speed pitches.
Changeups are a common type of off-speed pitch. They look very similar to a fastball -- they are thrown in a similar way and have a straight path -- but are significantly slower than a fastball. While fastballs are usually 90 MPH or above, changeups are usually only 70-80 MPH.
Why Are Changeups So Effective?
For batters, it is often difficult to detect the difference between a fastball and a changeup, since they have the same path and the speed of the baseball cannot be determined until it is very close to the batter. That is why changeups are so effective: They trick batters into thinking the pitch is a fastball, and the batter will swing at it. However, since changeups are much slower than fastballs, the swing would be too early, either missing the baseball completely or hitting it weakly.