How to throw a fastball

Here's how to throw a four-seam fastball. You want your fingers a little bit apart. Preferably on the other side of the seams so when the ball comes out you have resistance to throw against. It's firm with the fingers but should be somewhat of a subtle wrist. You don't want to be stiff.

A little space in here [between the palm of the hand and the ball].

The thumb almost bisects [the index and middle finger].

The movement would be straight. Four seams rotating out of your hand. The guys who throw hard, it's going to seem like the ball takes off.

Here's the two-seam fastball. Notice how the index and middle fingers are places directly on the narrow seams, not across them. Many pitchers have good success at getting a little more movement on their fastball with this grip than with a four-seam grip.