第一教 · Dai Ikkyo
Uki Goshi 浮腰
Floating Hip
Mechanic
Tori slips his hip in front of uke's and, with an arm around the waist, twists. Uke doesn't get lifted so much as whirled around the hip, which acts as a post his body wraps around on the way to the floor.
Analogy
You push into a revolving door in a hurry and lean into the bar. The door takes your push, spins on its axis, and whips you around with it, slinging you sideways out of the doorway before you can get a foot under you.
Why it maps
The door's central axis at hip height converts your straight-ahead push into a fast rotation around it, just as tori's inserted hip turns uke's forward pressure into a wrapping spin to the floor.