An impingement occurring between the deep side of the supraspinatus tendon and the posterosuperior edge of the glenoid cavity was evidenced in a young sports thrower presenting with a partial tear of the deep side of the tendon. This impingement occurred when the arm was in abduction-retropulsion and in forced lateral rotation. It was visualized on arthroscopy. The semiology was mixed, including signs of anterior instability and cuff impairment. The possible causes of partial tears of the deep side of the supraspinatus are discussed: sub-acromial impingement of NEER, anterior instability with secondary impingement, postero-superior glenoid impingement.