第一教 · Dai Ikkyo
Hiza Guruma 膝車
Knee Wheel
Mechanic
Tori places the sole of his foot against the side of uke's knee, fixing it in place, while his hands pull uke's upper body around and over. The stopped knee becomes the axle and uke's whole body wheels over it.
Analogy
A kid on a bike rolls into a low curb. The front wheel stops dead, but the rider doesn't: the bike pivots over the jammed wheel and the kid sails clean over the handlebars.
Why it maps
A low fixed block (the knee, the stopped wheel) becomes a pivot while momentum above it keeps going, so the body rotates over the block like a wheel around its axle.