I will state right here that there is no NATIONAL ASA/ISA rule on this topic. In Pennsylvania, there is a limitation. "On the Backswing, no part of the pitching arm or ball can be above your shoulder unless you bend at the waist." However, other than the ball being outside the wrist, this is perhaps the next most important difference between 9-Man and 10-Man Pitching.
The Humereus/Torso angle should not be greater than 90 degrees. This angle can be determined by drawing a line from the hip socket to the shoulder socket. Then draw a line, 90 degrees from that line as shown in the following images.
The only way to have a >90 degree angle is to rotate the humereus clockwise (thumb up/palm out) or raise the humereus laterally (away from the body).
