I know it's not exclusive to Ryan Hall and has probably been around for
a long while but I did notice he was using it alot during his match with
Matamoros.
While passing the guard he will throw a leg in an opposite direction of
it's side over his opponents leg and immediately roll over and under to
take his opponents back.
Looks like he did what Eddie would call a "Ninja Roll". He just used the pass basically to grapevine Matamoros' right leg, then did the "Twister Roll" from there to attack the back. Mastering the Twister Pg.89.
I think a variation of that move is on the Marcello Garcia gi set. You start off in half guard facing the opponent's legs (like marcelo likes to do) then when your opponent bridges into you you push down on your opponent's far leg and make a hook with the leg that was not trapped in half-guard.
daniel moraes breaks it down in his instruction that he made with world martial arts...www.groundfighter.com you can pick up the set cheap. he teaches it from the half guard in detail.