Golf is a sport with much repetitive actions often causing overuse injuries. We report a case of a left side avulsion fracture of the anterior serratus at the insertion on costa 4-6. A professionel golfer experienced sudden onset of pain of the chest during a golfswing. Clinically the patient had winging of the scapula and pain at the lateral side of costa 4-6. Ultrasonography showed an avulsion fracture of costa 5 at the insertion of the anterior serratus. The patient was referred to scapula-stabilising rehabilitation and fully recovered.