This pattern features a swift horizontal carry that slices between the other two balls. There is an assymmetrical version which is the most common & a symmetrical version which is not so common.
The Assymetric Version
Start with all three balls & juggle Two in one hand in a columns pattern while holding the third ball at the side with the palm of your hand facing down. You should have two balls going up & down in two seperate columns, one near the centre of the body & one on the outside. Throw the ball in the centre column a little higher than normal then do two things. With the same hand catch the ball in the outside column carry & throw it up on the other side of the centre column as an Under the arm throw, then catch the centre ball.
At the same time carry the ball you've been holding straight across to the other side, under the ball in the air & over the other arm as it scoops. Make it a real sharp straight slicing movement. Stop when your hand reaches the outside column of the two in one hand juggle. Wait until the ball thrown under the arm peaks, then toss the ball straight up in the outside column then Claw catch the under the arm throw. Resume the two in one hand juggle & just hold the third ball in your other hand.
Keep practising one slice at a time as described above. When it starts to feel more natural try slicing under every third throw of the central ball. Then move on to slicing under every second & for the full assymmetric pattern slice underneath every single throw of the middle ball.
Learn this trick on both sides so that you can easily move on to...
The Symmetrical Version
A bit slower but uses both hands equally.
Start with a two in one hand juggle as before & do a slice. When you claw the under the arm throw carry the ball down scoop it under the ball in the central column & throw it up on the inside. Then with the other hand make a slice underneath this throw. Toss the sliced ball straight up & claw the ball thrown under the arm & just carry on.