Penman's Box (unofficial name)
is a three ball pattern that can be thought of as either a variation of
Penman's Pandemonium (with which it shares a siteswap) or a variation of the
Box (with which it bears structural similarity). Either way, Penman's Box is
a fairly elegant trick that adds dynamic to the normally rigid Box pattern
with flourishing arm motions and underarm throws. If you are already
familiar with Penman's Pandemonium, this trick should be very simple to pick
up. However, this tutorial will assume you do not already know Penman's
Pandemonium (though you should be able to do the Box).
To learn Penman's Box, start with two balls in your dominant hand and one ball in your non-dominant. Make a vertical throw from your dominant hand and then, as that ball begins to descend, cross your non-dominant hand under your dominant hand and make a vertical throw along the outside of the first throw. This will clear space for your non-dominant hand to catch the first ball. As that second vertical throw is being made, swing your dominant hand up and over the first ball as it is descending, weaving your hand in between that ball and the ball just thrown from your non-dominant hand. Once your arm has returned to its normal position, catch the second ball in your dominant hand.
Practice this on both sides. Once you are comfortable with the vertical throws and arm flourish, you can add in the horizontal pass. Start by doing the same throws from the previous step and then, after you finish the arm flourish, you are going to make a vertical throw from your non-dominant hand (which should now be uncrossed). Simultaneously, you are also going to make a horizontal pass from your dominant hand to your now empty non-dominant hand, clearing space for your dominant hand to catch the underarm vertical throw made by your non-dominant hand. Then catch the third vertical throw with your non-dominant hand.
As shown, practice this on both sides. To run the full Penman's Box, just make another under-the-arm vertical throw (with your dominant hand this time) after the last vertical throw of the previous step. This will then be followed by an arm flourish and horizontal pass from your non-dominant hand.