EMPLOYEE WAS SWINGING AN 8 LB HAMMER WITH ONE HAND WHILE HOLDING A PUNCH WITH THE OTHER. HE WAS DRIVING OUT A WEDGE ON A TOOTH ADAPTER ON A COALSHOVEL DIPPER. WHILE SWINGING THE HAMMER. HE FEL T PAIN IN HIS SHOULDER. HE HAD INJURED THIS SHOULDER BEFORE BUT HAD BEEN FULLY RELEASED FOR WORK.