Chops is simply Under the arm on every throw but with an exaggerated carry.
Throw a ball under your arm, look at the way the arm you're throwing under instinctively moves out of the way. It should only be a tiny dodging movement for a regular under the arm throw, but in chops you extend that little movement into a long & fast diagonal chop from your shoulder to the opposite hip.
Juggle a Cascade, pick a ball & throw it under the arm every now & then. But instead of waiting for the chosen ball to fall into your hand, position your catching arm so that the elbow is pointing diagonally down to a point in front of your feet & so that your forearm is held vertically with your hand at the point where the ball will peak (about shoulder height). Catch a ball at its peak then imagine that your arm is like the windscreen wiper of a car & swiftly chop it diagonally down in a curve, your arm should swipe down 'flat' to your body, as opposed to away from you. Then throw it straight up under the arm. That is one chop.
Practice the chop on one side at a time until you are comfortable with it. Then work up to chopping on every throw. In the full pattern your arms will spend most of their time flat to the body, so there will be no arm sticking out to throw under. All throws are made from just above the opposite hip & pass in front of the downward chopping arm.