The "single leg" that I'm taking about is to use
- one hand to pull your opponent's leading leg.
- another hand to push his neck/shoulder/face.
There are many ways to finish with a "single leg" take down. You can:
- smash the back of his head on the ground.
- drop your forearm across his neck.
- drop elbow straight down on his heart area.
- drop your knee into his groin area.
- ...
You can also:
- hold on your opponent's leading leg.
- use leg to hook his rooting leg off the ground.
Since he will have no leg on the ground, he will fall with head on the ground first.