EMPLOYEE HAD JUST RETURNED TO THE DOCK, AFTER MEETING W/DREDGE OPERATOR. HE HAD DIS-EMBARKED FROM THE JON BOAT & JUMPED OVER SOME ROCKS THAT WERE ON THE DOCK. WHEN HE WENT INTO THE UPWARD MOTION TO JUMP THE PILE OF ROCK, HE FELT A ""POP"" IN HIS RT. CALF. WHEN HE STEPPED DOWN ON HIS FOOT, HE FELT AN EXTREME AMOUNT OF PAIN IN HIS CALF.