ALLEGED INCIDENT WAS SUPPOSED TO OCCUR WHILE EMPLOYEE WAS WALKING ALONG THE 1 WEST BELT. HE SAID HE TRIPPED OVER A LARGE ROCK AND SPRAINED KNEE; CAUSE OF INJURY--UNAWARENESS. MINER PROFICIEN CY A FACTOR; COMPLIANCE W/RULES, PROTECTIVE EQUIPMENT, MINING EQUIPMENT/SYSTEMS NOT FACTORS.