There are four main reasons for the pain behind the right shoulder: 1. It may be due to a strain on the infraspinatus and teres minor muscles in this area, for example, when the shoulder joint is rotated externally with force, it may cause the muscles to contract violently, resulting in a strain on the muscle tissue, thus forming edema and bruising, which will stimulate the peripheral nerves around it and cause pain; 2. If the upper extremity is kept in external rotation for too long, such as lifting or carrying heavy objects and the upper extremity is kept in forward flexion and internal rotation, if the upper extremity is kept in external rotation at night, it will lead to continuous fatigue of the infraspinatus and teres minor muscles and gradually form strain and inflammatory lesions, which will also lead to pain; 3. Tension, resulting in the accumulation of inflammation, slow blood circulation, resulting in pain; 4, suffered from external collision, external collision will lead to skin, subcutaneous tissue, muscle, fascia and other soft tissue damage, and therefore will produce pain.