What is the trajectory of a curveball, and how do pitchers normally throw it?
Steps:
1. Hide the ball in your glove.
2. Grip the ball with your middle and index fingers perpendicular to the seams at their widest point, with your thumb underneath the ball.
3. Spread your top fingers apart slightly and keep your ring finger and pinkie tucked into your palm. (Image 1)
4. Hold the ball firmly, applying pressure with your middle finger and thumb. Try not to let the ball rest in the palm of your hand, and keep your index finger relaxed. (Image 2)
5. Wind up into the pitch. Use the same pitching motion as in your other pitches so that the batter cannot predict a curveball. (Image 3)
6. Keep your wrist relaxed. After drawing back the pitch, hold your wrist so that the back of your hand points toward your body. (Image 4)
7. Roll your wrist downward and to the right (if you are right-handed) or to the left (if you're left-handed) immediately before releasing the pitch. (Image 5)
8. Release the pitch and follow through by bending your wrist. A right-hander should finish with the palm facing in toward the chest. The top of your thumb should be facing up.
9. Throw the ball between the batter and home plate if you're a left-handed pitcher facing a left-handed batter or if you're a right-handed pitcher facing a right-handed batter.
Easy curveball
The easiest way to throw the curve is to grab the ball with your fingers together. The grip can help you get more break out of your curve, but that is not the key. When you are throwing the ball the motion is just like a fastball. That is very important if you want to avoid putting extra stress on your arm. The only difference to the fastball pitch is that your palm should be toward your head (ear) at the point of release. Now that your palm is toward your head, instead of throwing the ball, think of karate chopping your hand toward the plate. This will keep a natural, easy motion and impart the correct spin (top spin slightly off center) to the ball.