At the end of the third step, when the right foot is forward, the ball is at the top of the back-swing. Note that my wrist has not turned.
7 Fourth Step
Up to here you have generated and stored power—and now you are ready to release it. At the start of the fourth step (A) the weight is on your right foot. Your right arm and left foot move forward simultaneously. As the step, generally referred to as a "slide," continues (B), some of your weight shifts to the ball of your left foot, but the right carries most of the load. The right, in fact, pushes your body forward as you slide on your leather-soled left shoe. Now (C) the weight gradually is taken by the left foot; the right's work now is mainly to balance.
Your left foot in the above figure (C) should be on the same board that you started from when you addressed your target, 12 feet and four steps ago.
8 Slide and Stop
Experts generally consider the complete "stop" either as the end of the fourth step or as part of the "release." It is treated as a separate stage here because few bowlers are aware of the pitfalls at this critical point. During the fourth step, your weight has gradually shifted to the ball of your left foot. Now, your right foot gives a final push and leaves the floor. Your entire weight is on your left foot. Your left arm and right foot help balance you. As your right arm, accelerated by the weight of the ball, catches up to your left foot, you apply weight on the left (rubber) heel, bringing you to a stop. This is the point at which the ball starts sliding off your fingers.
This is the crucial moment, the split second in which our previous moves are dramatized. It is too late to turn back.
Note, in figure at left, that ball, arm and toe are still at right angle to foul line as the ball is released.
9 The Release
Now that we have reached the crucial point in delivering the ball, let us review what we have done—and why. The mechanics will come easier if you understand the reason for each move. The idea, oversimply stated, is to start from 12 to 15 feet behind the foul line, approach the line, then roll the ball so that it will knock down all the pins. To do this with any degree of consistency, it is necessary to bowl in exactly the same way every time; in other words, keep the ball in the same arc. The key actions to meet this objective are: swing your arm freely, in pendulum fashion, and approach the foul line in a straight line with your eyes on the target and shoulders parallel with it. Thus, while addressing the target pins I consciously place the ball to my right side—by first breaking my line of vision to the target. This forces me to pause. Before adopting this measure, I used to hurry to the foul line, pushing the ball out and to the right as I stepped forward, with the result that the ball often wound up either behind me or too far from my body. Your arm cannot act like a pendulum every time unless its initial forward movement (first step) is directly to the front. The wrist also affects this motion. If your wrist is too loose, the weight of the ball will sway your arm from its intended path. The drawings on the left show how slightly my wrist turns during the entire delivery. From address to just before release it holds the same position (A). I start releasing the ball at the precise moment that the ball, which has been on a downward arc through the fourth step, reaches my left foot. The thumb comes out first. I "lift" the ball with my fingers, which gives my wrist a natural turn (B) of an inch or so. My hand continues its upward swing after the ball has been released. Thus, the ball crosses the foul line on an upward arc. Many good bowlers twist or snap their wrists upon releasing the ball. Do not try to copy them. They merely are compensating for some other bad habit, or sacrificing accuracy for unnecessary power. You do not need a wide, or sharp, hook to knock down pins.