A slider is a breaking pitch that is thrown faster and generally with less overall movement than a curveball. It breaks sharply and at a greater velocity than most other breaking pitches. The slider and the curveball are sometimes confused because they generally have the same purpose -- to deceive the hitter with spin and movement away from a pitcher's arm-side. (When a pitch seems to toe the line between the two, it is referred to in slang as a "slurve.")
Most professional pitchers possess either a slider or a curveball -- and some possess both breaking pitches. Having a breaking pitch, like a slider, is an essential component to a professional starter's arsenal, because it keeps the hitter a bit off-balance and unable to commit to gearing up exclusively for a fastball.
A slider is meant to be slightly more deceptive than a curveball because it is thrown harder and has spin that more closely resembles a fastball -- although it doesn't create as much overall movement. Many power relief pitchers possess only a fastball and a slider in their arsenals -- with one pitch setting up the other because of the late deception created by the slider.
Like a curveball, a slider is thrown by a pitcher with a wrist snap and spin. It is generally perceived as somewhere between a cutter and a curveball. A slider that doesn't break as much as a pitcher hopes is referred to as a "hanging slider" or a "hanger" and is much easier for the batter to hit because of its straight trajectory and sub-fastball velocity.
Watch: John Smoltz demonstrates how to throw a slider.
When the slider first came to prominence in the first quarter of the 20th century, it was referred to as a "nickel curve." There is no consensus as to who invented the pitch; however, aptly named Hall of Famer Charles Albert "Chief" Bender is widely believed to be the first to bring the pitch to prominence.
In A Call
"snapper," "slide piece," "breaking ball," "sharp breaking ball"