The kao/bump/shoulder reminds me of charging in basketball. In this video, Shane Battier explains how to take a shoulder charge to draw the foul. Of course he is falling down on purpose, even explaining how the sweat makes you slide on the hardwood, but flipping the intent of the video around, there are several nice examples where the dribbler could be doing kao with the shoulder as a deliberate knockdown. I asked a couple of my judo senseis if this move would be legal in shiai and they said probably not depending on the referee. Still, I will try it in randori, at least as a sort of ouchi gari or kouchi gari, if not the outright obvious bump.

Taking the charge