Goal:
To throw with exactly the same arm speed as normal fastballs but with pressure on the outer half/third of the ball, creating a late cutting motion. You want the hitter to see fastball out of the hand, with the speed and spin, so that he commits a tad early and causing him to miss the sweet spot on the bat
Grip:
These pitching grips are extremely similar to normal fastballs. Middle and Index fingers have mostly no space in-between them and they are placed outside the center of the ball, respective to left-handers and right-handers
Hand Action:
There is no real change in the motion of the hand but there can be a slight supination (turning the hand in towards the head). This will help to make sure that when the ball is thrown the force is applied to the outer part of the baseball. In essence, that will naturally cause the abnormal spin on the outer half creating the desired movement away from the pitching arm side
Predicted Movement:
The desired movement on this pitch is very slight. You want to maintain close to normal velocity and to do that, the ball can not move more than 3-6 inches. You shouldn’t want more movement than that. Remember, the cut fastball isn’t designed to be a breaking pitch (i.e. curveball or slider)
How To Grip It...
Place the middle and index fingers to the outer third of the ball, with no space between them. As far as finger placement on the seams, one possibility is just moving the fingers to the outside part of the seams you use for your 4 seam fastball grip (picture on the left). Another possibility is to place the middle/index fingers in line with the seams like you would a 2 seam fastball but higher up (see Picture on right).
4-Seam Cut Fastball Grip...