Ushiro Goshi is attempted as a counter when ones opponent is turning in for a hip throw or should throw. Here, Uke is attempting Tsuri Komi Goshi and Tori is reacting 'instinctively' to Uke's attack by dropping his hips in Jigotai. He then drops his hips even further and then lifts Uke up by thrusting his hips forward and bounching Uke off the ground into the air before bringing his down to Uke's rear.
Here you can see the key components of this throw frame by frame:
This is one of his favourite throws. Being a tall solidly built man, he has lots of power to utilise with this throw when an opponent attempts hip or shoulder throw on him.