THE TRAILER RECEIVER WASN'T SEATED PROPERLY ON THE BALL. EMPLOYEE BENT DOWN PLACING LEFT HAND ON THE TRAILER, RIGHT HAND ON THE BALL (HITCH AREA). UPON BENDING DOWN THE WEIGHT SHIFTED APPLYING MORE WEIGHT TO THE TRAILER. RELEASING THE RECEIVER DOWN ON TOP OF THE BALL. THE RECEIVER CAUGHT THE LEFT SIDE OF THE EMPLOYEE'S RIGHT INDEX FINGERNAIL.