[header] How to throw a curveball [title] Grip the ball between your thumb and middle finger. [step] Place your middle finger along the bottom seam of the baseball and your thumb along the back seam. Leave your index finger off the ball. 
Instead of using it to grip the ball, you'll be using it to point at where you want the ball to go. [substeps] Hold the baseball such that the curves of the seams are close to your palm, with one on top and one on the bottom of your palm.