Just to reiterate, this is just the interpretation going on in my neck of the woods. Someone else would say something completely different.
I believe you are referring to o-gyaku from Koto ryu, a drop of the hips to root against a throw followed by a strike to his hips and then a punch to the sternum or ribs when he's off-balance. Shinden Fudo ryu also uses a strike to his hips following the root (literally written as a slap in the translations of densho I have).
Let me know if you find out any more about these!