A humeral fracture. The upper arm (medically termed the 'arm') contains one bone: the humerus. In basic terms, you can have a humeral head/neck fracture, proximal, mid-, or distal shaft fracture, or an epichondylar fracture. There are also grades of fractures indicating the amount of separation, splintering, etc, but this goes beyond your question of 'breaking the arm bone'. The forearm contains the ulna and radius. Don't get that confused with the arm. He didn't break his arm. He tore ligaments around his rotator cuff, possibly the scapula sling, and maybe even his brachial plexus. Not a fun injury, I would rather have a broken arm, or, more specifically, a humeral fracture. Source: I am a doctor.