It's similar to a move that we call a "Metzger".
I don't know who Metzger is/was.
The move is a counter to a single leg.
When your leg is off the ground in a single position, you hook behind your opponents far knee with your trapped leg.
Grab your opponents far shoulder or even around the waist and pull back while lowering your level and hooking behind your opponent's other knee with your other arm. You sort of sit to your hip and drop your opponent to his back.
I hope this makes sense. Maybe someone could explain better?