Can you guess what this trick involves? Not the catchiest of names I know. I learnt this trick from George Gillson's book, Beyond the Cascade & he called it the above so it has just stuck.
The main feature of this trick is a throw made Under the arm that goes Over the top of the pattern & is caught with an Under the arm catch so practise it with just one ball. Cross your arms over with the ball in the lower hand. Toss the ball all the way to the other side. While the ball is in the air uncross & recross your arms before catching the ball with the opposite hand to the one that threw it. If you can already do other crossed arm tricks this may be a simple step but one worth spending a little time on. Focussing on this throw in the full pattern helps you to maintain the pattern rather than lapsing back into Mills Mess for example. Practise throwing from hand to hand in this way.
Now with all three balls, juggle a cascade & with one hand throw a short vertical throw to the same height as your other cascade throws, then throw the next ball under the arm as you have just been practising. The other hand crosses over the top of the under arm throw to catch the vertical throw. Make it a nice high throw to give yourself time to figure out what you need to do underneath it.
If you freeze the pattern immediately after making the under arm throw, you should be in a position where one ball is in the air, your arms are crossed over & each hand is holding one ball. In the one ball exercise when the under arm ball was in the air you uncrossed & recrossed your arms before making the catch. Now do exactly the same, uncross your arms carrying each ball. When your arms are uncrossed throw the ball in the hand that was on top as an over the top throw in the same direction of the under arm throw so that it lands in the centre of the pattern. Then recross your arms, the empty hand goes under to catch the under arm throw. The other hand goes over & throws another short vertical throw. After this go back into the cascade.
Practise this move starting with each hand alternately. Start off throwing the under arm throws really high so that you have time to think about what happens underneath. With practise you will be able to perform the uncrossing & recrossing bit without thinking. When you are comfortable with the move, reduce the height of the under the arm throw.
The short vertical throw made by the top hand when your arms are crossed over brings you back to the beginning of the pattern. Carry on by throwing another under the arm throw back over the top of the pattern & just keep going. Focus your attention on the ball thrown & caught under the arm. It is very easy to break out of the pattern & fall into something more familiar but this is a rare pattern where you can throw high & take it slowly & actually think what you have to do next to keep the pattern going.