To grip the four seam fastball, place your index and middle fingertips directly on the perpendicular seam of the baseball. The “horseshoe seam” should face into your ring finger of your throwing hand (as shown in the picture on the left).
Next, place your thumb directly beneath the baseball, resting on the smooth leather (as shown in the picture on the right). Ideally, you should rest your thumb in the center of the horseshoe seam on the bottom part of the baseball.
Grip this pitch softly, like an egg, in your fingertips. There should be a “gap” or space between the ball and your palm (as shown in the middle picture). This is the key to throwing a good, hard four-seam fastball with maximal backspin and velocity: A loose grip minimizes “friction” between your hand and the baseball. The less friction, of course, the quicker the baseball can leave your hand.