WHILE UNLOADING ANFO EMPLOYEE BENT OVER AND LEANED DOWN TO HIT THE LOWER PADS ON THE TRAILER TO LOOSEN THE ANFO WITH RUBBER MALLET. AS HE STEPPED BACK TO STAND UP HE STEPPED ON A ROCK CAUSING HIM TO FALL BACK AND TWISTING HIS RIGHT ANKLE. HIS ANKLE STARTED TO SWELL AND TURN PURPLE.