Under the Arm
Each time a club is thrown under an arm it comes up on the outside of that arm and is caught in the usual way. The clubs should be thrown as near as possible to the body plane and slightly forwards. The arm under which you throw should be locked straight and pointed downwards to keep your elbow out of the way, this is especially important if you attempt continuous under arm throws. You should also lean forward slightly to give the clubs more room to pass. As with all body throws, hold the clubs at the bottom of the handle near to the knob. The clubs should pass under your arm at a point just above the elbow.
Later on I describe a trick called chops in which each club is swung rapidly downwards and across the pattern before being released, it looks very different to this trick but it is essentially the same pattern, the difference being that the problem of your elbows getting in the way is dealt with by quickly pulling your arms up and over the clubs, rather than by straightening them out.
Under the arm throws look very good from the side, especially if you throw the clubs forward a little. If you can do continuous single backcrosses as well as continuous under the arms then try going from one trick to the other and back - when done smoothly, I think this sequence is one of the nicest club tricks that there is.