The Frantic Cascade
(unofficial name) is a three ball variation of the Crossed-Arm Cascade in
which every catch is made under-the-arm (or more accurately
under-the-wrist). This leads to a very quick pattern as your hands rush to
catch each ball. The name "Frantic Cascade" is one of my own creation,
since the trick is otherwise often referred to by the lengthy "crossed-arm
cascade with continuous under-the-wrist catches." Before learning this
pattern, it is important that you already be able to juggle the regular
Crossed-Arm Cascade using both arm configurations.
To begin learning the Frantic Cascade, start with two balls in your dominant hand and one ball in your non-dominant. Cross your dominant arm over your non-dominant arm and then make a throw from your dominant hand toward the dominant side of your body (as if doing the Crossed-Arm Cascade). Follow this up with a corresponding throw and catch from your non-dominant hand. So far this has all been identical to the Crossed-Arm Cascade. However, as the ball thrown from your non-dominant hand begins to descend, you are going to make another throw from your dominant hand and then quickly uncross and recross it underneath your non-dominant hand, catching the ball thrown from your non-dominant hand. The ball just thrown will then be caught by your non-dominant hand.
As shown, practice this on both sides. Next, you are going to add in another throw/under-the-wrist catch combination, this time from your non-dominant hand. As the last ball thrown in the previous step begins to descend, make a throw from your non-dominant hand and then uncross and recross your non-dominant hand underneath your dominant hand (i.e. in the same position as you first started), catching the descending ball under-the-wrist.
Practice this on both sides. To run the full pattern, simply keep making throws paired with under-the-wrist catches. The Frantic Cascade will take some time to master, as it has a very rapid pace.