INJURED WAS OBSERVING ELECTRICIANS WORK ON TAILPIECE OF LONGWALL. THE ELECTRICIAN WERE PLUGGING GAUGES INTO STAGELOADER PANEL. A CO WORKER STARTED TO PUSH THE HEADGATE CAUSING THE TAILPIECE TO MOVE INJURED RUSHED TO STAGELOADER TO HIT THE EMERGENCY STOP BUTTON. INJURED STEPPED IN A HOLE TWISTING HIS KNEE.