In football, linemen use a technique called “the rip.” You can watch the video here (pop-ups warning), even though it may not be clear. Imagine the opponent’s arms at your shoulders. Your right arm comes slashing upward, intercepting his right arm diagonally. This move not only gets his hands off of you, but angles you to his outside.
The $60,000 question: How can this be applied to the big stick?
Imagine an opponent who grabs both of your shoulders. Keep in mind he will not just stand there, but the hands on the shoulders is a prelude to pushing, pulling into a knee, a push and punch, etc. In rifle grip, bring up the left end of the weapon diagonally, coming up from the outside of the opponent’s right elbow. This movement can be repeated, coupled with right butt end strokes to his ribs.
Move to the outside and slam, hitting him with the portion of the stick between the hands.