Sweeping Hip Throw
According to Jigoro Kano, Shiro Saigo, given a little time, could always devise a counter attack to get out of any technique applied against him. Since Kano was good at the uki-goshi, for a good while Saigo could not get the best of him, but later he figured out a method of jumping forward and getting away. Professor Kano devised a way to prevent this escape. The way he would sweep and stop his opponent’s escape foot is the origin of the present harai-goshi.
The best book on this throw is Harai Goshi by Jean-Luc Rouge, one of the Ippon Judo Masterclass Series. It is an excellent book dedicated solely to the technique harai goshi. It explores grips, variations, entries, combinations, and self-defence applications, by a world champion judoka.
Here are some animations. Here is a video of harai goshi performed by Neil Ohlenkamp (tori) and Gordy Oliver (uke) of the Encino Judo Club. Here is another video of harai goshi and a second video of harai goshi.