video / animation
These show what happens to the shoulder during the throwing motion when the posterior-inferior glenohumeral ligament is normal, and when it is too tight. You can see how a tight PIGHL damages the labrum. In these models, all ligaments have been removed, except the PIGHL (posterior-inferior glenohumeral ligament). Remember, that is the one that gets tight in throwers.
NORMAL throwing motion:
ABNORMAL throwing motion:

Watch here how the ball stays centered in the socket during the entire throwing motion.

This is the throwing motion of a shoulder with a tight PIGHL. See how the ball rides up and back (postero-superior) on the tight PIGHL. Over time, the humeral head will shear the posterior-superior labrum right off the bone!