On the left is a hook ball (moves right to left) thrown
by Coral Bolton. On the right is a backup (moves left to right) thrown by
Debbie Kawchuk.
You want to release the ball off the end of the fingers
with the ball beside the sliding foot. Notice that the sliding foot is
pointing straight down the lane. This acts as a guide for the ball.
In both pictures the feet are aligned and the arm is perpendicular to the floor
at the release. If the hand is directly behind the ball on release,
the ball will follow a straighter path to the pins than if the hand is off to a
side.