This type of catch is familiar from disciplines such as Static Cradle or Korean Cradle, but is rarely seen in flying trapeze. The grip on the ankles is worse than is possible on the legs or wrists, and the forces on the catcher while swinging mean it is more difficult to hold onto the flyer than when the catcher is static (in a Cradle act). As such, it can be quite dangerous.
Reverse Ankles is far less common than the already rare Ankles catch because of the paucity of tricks that result in the flyer being in the right orientation. The flyer must be facing downwards at the point of the catch. The best example is a Reverse Back Somersault.
You can find out more about this trick in my books:
Thanks to the team at Circus Arts Australia for providing this video.