11. A 14-year-old rugby player comes into the office two weeks after he dislocated his right shoulder during a rugby game. The shoulder self-relocated upon examination by the athletic trainer at the game; however, he was unable to continue playing. He was sent to the hospital as a precaution where he was assessed and discharged with medications, an arm sling, and instructions to go for rehabilitation. Upon chiropractic examination, the chiropractor finds that there is atrophy in the deltoid, weakness with elbow extension and shoulder external rotation. What peripheral nerve was damaged as a result of the shoulder injury?