Ushiro Goshi is a great throw because it is essentially a counter to a hip throw.  To begin, tori and uki faceoff in kumi kata position.  On the right side, when uki attempts to come in for a hip throw, tori bends his knees and straightens his back.  At the same time, tori places his left arm around uki’s hip while still holding the lapel.  The throw is executed by driving your stomach forward, straightening up and driving up with your left knee under the uki’s butt.  Note: (The illustration above does not clearly show the driving of the knee which is perfectly correct, but the knee helps make the throw more devastating).  Right arm helps in slamming uki on to the mat flat on his back.  This is a tough throw for the uki to take if tori executes properly.  Important Note: This is a timing throw.  It must flow properly or it can not be executed.  So as soon as the uki attempts the hip throw, tori must do all of the things listed above simultaneously.  The flow gives the tori momentum and makes the throw possible.