I will state right here that there is no ASA/ISA rule on this topic. 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).
