The hook is a spectacular but rarely seen move, in which the juggler traps the handle of a club against his arm using another club, and then flicks it outwards so that it flies into the air.
It is usual to start from a club on a club balance, although I will explain another method later. Give the balanced club a little push upwards, so that it hops up a few inches while remaining vertical. Move your arm forwards so that as the handle comes down again you can trap it against your inside wrist using the handle of the second club, as shown:
As soon as you have done this allow the club to topple inwards, while maintaining your grip. Twist your forearm outwards in a small arc, so that the club continues to travel in a circle, as indicated by the arrows in the previous diagram. Keep the club's handle trapped until the body starts to swing upwards again, then release your grip.
The club should come back over to your other hand, spinning as if it were an outside flat throw. Be warned, if you release the club a fraction of a second too early or too late, the consequences can be frightening - it is likely to shoot off at a wild angle, often with surprising force. Be gentle with the hooking action when you are learning. If you are having difficulty controlling the throw then try allowing the balanced club to lean inwards a little before you hop it into the air. This should mean that the club is tilting when you trap it in place; now the club has a smaller angle to swing through before it is released, resulting in less momentum at the end of its swing, making it easier to control. The club which is 'hooked' should be gripped near the end of the handle, so that the knob is preventing it from flying off.
The release should happen almost automatically - as you turn your arm outwards a gap will naturally open between the restraining club handle, and your forearm.
The main thing with this trick is to make it as slow as possible, think of it as a swing of the arm, rather than a flick of the wrist.
You don't have to start this trick from a balance - anything that gets the club vertical and in the right position will do. Try throwing a vertical floater or a small inside flat, and trapping the handle in mid-air.