Just to add two cents, most of the players I work with have too much external rotation and not enough internal rotation. Most players that develop elbow issues have this exact imbalance: Internal Rotation Deficit. Not trying to be negative or argumentative in any way, but just what I have seen over 20 years. Not sure why a player would want to create that type of imbalance of ER to IR. additionally, it is not just the shoulder (glenohumeral joint) that allows these folks to get into these angles and throw as they do, but a combination of many things such as scapular positioning, spine angles, as well as the pelvis and hips. Again, just my two cents.