The slider is gripped similar to a two-seam fastball, with the middle finger and index finger across the two widest seams. The difference is that the fingers should be slightly off-center, toward the outside of the ball, like you're just holding the outside third of the ball.
Your thumb should be tucked under the ball, with the ring and pinkie finger off to the side.
Apply pressure to the ball with your thumb and middle finger.
Throw the ball the same way you'd throw a fastball. A common tip is to imagine cutting through the ball with your middle finger as you throw the pitch. The ball should roll off your hand off your index finger, which is what gives the slider its spin.
Don't forget to follow through. When you don't follow through, the ball will likely stay high.
The slider breaks late, making it one of the most effective pitches in baseball.
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