Dear Robin,
Tori enters to the side of Uke-lower hand grabs hold of ukes belt, maintains tight control of the uke via belt, inserts knee behind uke and drops[otoshi ] uke backwards over his knee.Obi [belt ]otoshi [dropping motion ].This method ensures a good connection between Uke /Tori .It a strong waza. Tori can also take ukes neck and control the neck in conjunction with the belt hold-a variation-slightly severe method here. Cheers, Joe.