Two-seam fastball
A two seam fastball, also known as a sinker or cutter (cut fastball), is gripped slightly tighter and deeper in the throwing-hand than the four-seam fastball. To throw a two-seam fastball take your index and middle fingers and place them directly on top of the narrow seams of the baseball (see below left, middle photo). Next, place your thumb directly on the bottom side of the baseball and on the smooth leather in between the narrow seams (see below right photo). The two seamer is gripped a little firmer than the four seamer. A firm grip causes Friction:( Ffrict = "mu"*Fnorm ). which causes the baseball to change direction. It also slightly reduces the speed of the pitch, which is why most two-seamers register about 1 to 3 mph slower than four-seam fastballs.
Four-seam fastball
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(see below right, middle photo). The term horseshoe comes from the red stitching that the seam itself looks like the shape of a horseshoe. Next, place your thumb directly beneath the baseball, resting on the smooth leather. You want to rest your thumb in the center of the horseshoe seam on the bottom part of the baseball (see below left photo). Your grip should be soft and held loose in your fingertips. There should be a "gap" or space between the ball and your palm. This is the key to throwing a good, hard four-seam fastball with maximal backspin and velocity. A loose grip minimizes friction ( Ffrict = "mu"*Fnorm) between your hand and the baseball. The less friction, of course, the quicker the baseball can leave your hand. Does a four-seam fastball rise? “No,” says Bill James, author of the The Neyer/James Guide to Pitchers.
“Fastballs can't rise unless it's thrown underhand. But if you throw the fastball overhand with enough force, it will appear to rise because it's not dropping as much as the batter's brain thinks it should.”
Split-finger fastball
A split-finger fastball sometimes called a splitter or splitty is an advanced pitch. Usually a pitcher with large hands excels throwing this pitch due to the fact that it sets deep in the palm of the hand. They refer to this as "choked" meaning deep in the hand. This is how splitters get their downward movement. Your index and middle fingers should be placed on the outside of the horseshoe seam. Grip the ball firmly. When throwing this pitch, throw the palm-side wrist of the throwing-hand directly at the target while keeping your index and middle fingers extended upward. Your wrist should remain stiff as if to be giving the peace sign with a baseball in your hand at release.
