Curveball

In baseball and softball, the curveball is a type of pitch thrown with a characteristic grip and hand movement that imparts forward spin to the ball, causing it to dive as it approaches the plate. Varieties of curveball include the 12–6 curveball, power curveball, and the knuckle curve. Its close relatives are the slider and the slurve. The "curve" of the ball varies from pitcher to pitcher.

The curveball is typically gripped in a manner similar to holding a cup or glass. The pitcher positions the middle finger along and parallel to one of the ball's long seams, while the thumb is placed on the seam opposite, forming a "C shape" when viewed from above, with the horseshoe-shaped seam facing inward toward the palm. The index finger is aligned alongside the middle finger, while the remaining two fingers are folded toward the palm, with the knuckle of the ring finger resting against the leather. Some pitchers may extend these two fingers away from the ball to prevent interference during the throwing motion. The grip and throwing mechanics of the curveball closely resemble those of the slider.

The delivery of a curveball is entirely different from that of most other pitches. The pitcher at the top of the throwing arc will snap the arm and wrist in a downward motion. The ball first leaves contact with the thumb and tumbles over the index finger thus imparting the forward or "top-spin" characteristic of a curveball. The result is the exact opposite pitch of the four-seam fastball's backspin, but with all four seams rotating in the direction of the flight path with forward-spin, with the axis of rotation perpendicular to the intended flight path, much like a reel mower or a bowling ball.

The amount of break on the ball depends on how hard the pitcher can snap the throw off, or how much forward spin can be put on the ball. The harder the snap, the more the pitch will break. Curveballs primarily break downwards, but can also break toward the pitcher's off hand to varying degrees. Unlike the fastball, the apex of the ball's flight path arc does not necessarily need to occur at the pitcher's release point, and often peaks shortly afterwards. Curveballs are thrown with considerably less speed than fastballs, because of both the unnatural delivery of the ball and the general rule that pitches thrown with less speed will break more. A typical curveball in the major collegiate level and above will average between 65 and 80 mph, with the average MLB curve at 77 mph.

From a hitter's perspective, a curveball initially appears to travel toward a specific location—often high in the strike zone—before rapidly dropping as it approaches the plate. The most effective curveballs begin breaking at the apex of their flight path and continue to break increasingly sharply as they approach and pass through the strike zone. A curveball that lacks sufficient spin will fail to break significantly and is commonly referred to as a "hanging curve". These pitches are particularly disadvantageous for pitchers, as their low speed and minimal movement often leave them high in the strike zone, making them easy for hitters to time and drive with power.

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. 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 a greater chance of throwing wild pitches when throwing the curveball.

When thrown correctly, it could have a break from seven to as much as 20 inches in comparison to the same pitcher's fastball.

Due to the unnatural motion required to throw it, the curveball is considered a more advanced pitch and poses inherent risk of injury to a pitcher's elbow and shoulder. There has been a controversy, as reported in The New York Times, March 12, 2012, about whether curveballs alone are responsible for injuries in young pitchers or whether the number of pitches thrown is the predisposing factor. In theory, allowing time for the cartilage and tendons of the arm to fully develop would protect against injuries. While acquisition of proper form might be protective, physician James Andrews is quoted in the article as stating that in many children, insufficient neuromuscular control, lack of proper mechanics, and fatigue make maintenance of proper form unlikely.