EMPLOYEE WAS PLACING PIN FLAGS INTO THE GROUND. AS HE WAS STRAIGHTENING UP FROM PLACING A FLAG HE NOTICED A PAIN IN HIS LOWER LEFT SIDE OF BACK. WITHIN 30 MINUTES HIS LEFT FOOT BEGAN TO TINGLE AND BECOME NUMB. HIS CALF MUSCLES BECAME TIGHT WHEN WALKING. HE WAS UNABLE TO WORK HIS SCHEDULED SHIFT ON 08/04/03.