The whip catch is one of the more impressive diabolo tricks & is often used as a finale trick. The diaboloist throws the diabolo into the air then while holding both handsticks in one hand he or she whips at the diabolo miraculously snagging it from the air. The best thing about this trick is that it is nowhere near as hard as it looks when you know how to do it.
Get the diabolo spinning then make a low Throw about 2 feet above your head that goes out to your subordinate side rather than straight up. While the diabolo is in the air pass your subordinate handstick into your dominant hand. Hold the sticks in a 'V' shape by placing your index finger in between them. Turn sideways to face the falling diabolo side on. Move & bend your arm up & back so that you are standing with your elbow pointing forwards & your dominant hand by the side of your head. Your hand should be holding the handsticks so that the loop of string is hanging over your shoulder. Make sure that you are holding the sticks so the tips are side by side & not one above the other.
In one smooth movement swing your arm down on top of the diabolo. Try & make the swing as big as possible, firstly it looks more dramatic, secondly the speed of the string flying through the air will make a very satisfying 'swishing' noise & thirdly it gives the string more time to form a clean untwisted loop. Throughout the swing make sure the tips of the sticks are side by side & not one above the other.
To make the catch you will need to make one side of the loop land on top of the axle while the other side needs to pass in front of the front cup. Imagine a line running from the diabolo's axle to your dominant hand. Continue the swing aiming to make the tip of the inside handstick pass in between you & the diabolo on the imaginary line. As soon as your handsticks have passed the diabolo stop the swing dead & allow the weight of the falling diabolo to pull the string tight leaving the diabolo hanging in a loop. Transfer your subordinate handstick back into your subordinate hand & resume diaboloing.
Once you have learnt the catch try whipping the diabolo after throwing it from a Basic rip off or a Trapeze rip off. Things can be made even more interesting by adding a pirouette or two in between the throw & the catch.