EE was stacking a pallet of rock when he was hit with a rock in the lower calf. When he got up he could not detect where the rock had come from. He told another EE & later his supervisor. He tried to walk it off but couldn't. Went to ER @ 2:30pm & was given CT Scan & Ultrasound, pain & swelling medication & told to Ice & Elevate leg. MRI scheduled & told not to work until cleared.