The large defect (arrow) in the posterosuperior margin of the left humeral head is in the classic location for a "Hill-Sachs" lesion, which is an impaction fracture seen in the humeral head due to anterior dislocation.
The prior film was taken during an episode of anterior dislocation, and nicely shows how the inferior margin of the glenoid fits into the Hill-Sachs defect on the humerus. If the glenoid is doing this to the humeral head, we can imagine that the head is also trashing the glenoid labrum, producing a Bankart lesion.