Skiponzo

Ellsbury subluxed (didn't dislocate, important distinction) his shoulder because it was in a forward flexed, abducted, externally rotated position and a fully grown male human being fell forcefully on his arm, causing his humeral head to abnormally translate across his glenoid, exceeding the load to failure of his anterior/inferior glenohumeral ligament/labrum complex NOT because he's "injury prone".