EMPLOYEE STATES HE WAS DRIVING #2 POLARIS 6X6 FROM PUMP #3 TO PUMP #2. AS HE WAS STARTING DOWN THE HILL HE LET OFF GAS THE EBS LOCKED UP CAUSING THE ATV TO SLIDE SIDEWAYS. THE FRONT END HIT A SNOWBANK & STARTED TO ROLL. HE JUMPED OFF CATCHING HIMSELF WITH HIS RIGHT ARM DISLOCATING HIS SHOULDER.