Driller was attempting to put a grading in place when EE lost footing and slipped through the area around the head on the drill. EE hit just under EE's knee with the grading that was already in place. EE's helper helped EE out and EE went to the first aid kit; saw it was a deep cut and called Supervisor who in turn called Safety to assist. Went to the ER and received 10 stitches.