EMPLOYEE WAS USING AN 8 LB SLEDGEHAMMER TO CLOSE A VALVE ON #1 SPENT LIQUOR PUMP. A PORTABLE STAND WAS IN CLOSE PROXIMITY, OBSTRUCTING HIS SWING PATH. AS EMPLOYEE WAS SWINING THE HAMMER IN THI S POSITION, HE FELT A SHARP PAIN IN HIS RIGHT SHOULDER. EMPLOYEE IS NOT LOSING ANY TIME BUT ISON WORK RESTRICTIONS.