The curveball is a type of pitch in baseball thrown with a characteristic grip and hand movement that imparts forward spin to the ball, causing it to dive in a downward path as it approaches the plate. Its close relatives are the slider and the slurve. The "curve" of the ball varies from pitcher to pitcher.
The curveball is a popular and effective pitch in professional baseball, but it is not particularly widespread in leagues with players younger than college-level players. This is with regard for the safety of the pitcher - not because of its difficulty - though the pitch is widely considered difficult to learn as it requires some degree of mastery and the ability to pinpoint the thrown ball's location. There is generally greater chance of throwing wild pitches when throwing the curveball.
Grip and action Edit
The curveball is gripped much like a cup or drinking glass is held. The pitcher places the middle finger on and parallel to one of the long seams, and the thumb just behind the seam on the opposite side of the ball such that if looking from the top down, the hand should form a "C shape" with the horseshoe pointing in towards the palm following the contour of the thumb. The index finger is placed alongside the middle finger, and the other two extraneous fingers are folded in towards the palm with the knuckle of the ring finger touching the leather. Occasionally some pitchers will flare out these two fingers straight and away from the ball to keep them clear of the throwing motion. The curveball and slider share nearly identical grips and throwing motion.