Release/back-side knee drive

The throwing arm should optimally be at a high-three-quarter position at release point for pitchers. That is, not straight over the top, not sidearm, but a notch higher than the midway three-quarter point. The hand should smoothly reach out and gain extension at the final moment of contact before the ball is released. The pitcher should also bend at the waist while rotating the hips.

Next, the hand and arm should follow through across the body, going to the outside of the front leg. At the same time, the back knee should pull forward a little, in order to make sure the back hip rotates.

Ellis Pitching Tips - stevenellis.com