The Basics of Throwing a Slider
A really valuable extra pitch is the slider--the fast ball curve or the nickel curve, as it is often called. The slider is actually a combination curve and fast ball. It comes full speed but it curves away from the batter (away from the right-handed batter if a right-hander throws it) just a little, often just enough to make him miss. Batters hate this pitch and pitchers love it.
A slider is thrown in almost the same motion a quarterback uses to zip a football downfield. But it is held the way you would hold a fast ball, putting pressure on with the middle finger. (In throwing a curve, the index finger holds most tightly). You deliver the ball not off the fingertips, as you do a fast ball, but off the edge of your finger, as you do a curve.
The difference is that instead of turning your hand completely over and following through with palm up, you cut the hand away swiftly, as when you throw a football, and bring the arm down with the palm facing first base (if you are right-handed). In every way--full stride, good shove off the rubber, full arm's length throw--you deliver this pitch as you do a fast ball. You should be able to control it quickly if you have learned to keep you fast ball low.