A forkball in baseball is a type of pitch that is similar to a curveball, but more extreme. Forkballs break downward, but their break is much more extreme and sudden than a typical curveball. They are a rare type of pitch due to the tiring and risky motion used to throw them.
Forkballs are a rare type of breaking pitch. They are like an extreme form of curveballs in that they break downward, but their break is much more extreme and sudden. Throwing forkballs requires the pitcher to snap his wrist, which can be tiring and may cause injury, and contributes to why pitchers rarely (if ever) throw forkballs.