The curveball grip is fairly simple and, unlike other pitches, allows a pitcher to maintain a good grip on the ball, and therefore, control, and throwing an effective curveball involves more than just your arm. There is no specific moment when a coach or parent will say it is time now to throw curving ball. However, the proper age for the player to be able to throw curving ball is 14 or 15 years old. If young players throw curveballs on a consistent basis at younger ages they can cause damage to their elbows and thus hinder the growth process.
The mechanics of throwing a curveball are completely different from a fastball. The path of the ball on a fastball is generally far from your head. In the case of a curveball, the path will be much closer to your head.
There are several key elements to the curveball that must be followed in order to throw the pitch properly:
First of all, start out by hiding your baseball in the palm of your glove. There is no need to advertise what type of pitch you are about to make. The same applies to your windup. Do not use it to advertise what you are about to do. Keep the batter guessing for as long as you can.
Grip the ball with your middle and index fingers together, with the fingers across the seams of the ball at the widest part (the widest distance between the seams). Keep a tight grip on the ball, especially with the middle finger. Don’t let the ball touch the palm of your hand, or you won’t generate enough topspin, which is what allows the ball to drop when it gets close to home plate.
Practice developing your speed as you master your form and stance. Speed is a very important factor in your delivery. Curveballs with little speed are easily hit by the batter as any batter that is any good will seek to determine the particulars of the pitch and respond accordingly. The more time the batter has to gauge the speed and angle of the throw, the easier it will be to successfully launch your curveball into the outfield
When releasing a curveball, your wrist will be hooked and your hand will pull down in front of your body. It is important that you release the ball close to your body (Short Arm). The further you release from your body, the less resistance your middle finger will have on the seam and therefore your rotation will be looser.