is one of the original 40 throws

Throw (grappling)

A throw is a martial arts term for a grappling technique that involves off-balancing or lifting an opponent, and tossing them to the ground in Japanese martial arts referred to as nage-waza, 投げ技, "throwing technique"...

 of Judo

Judo

is a modern martial art and combat sport created in Japan in 1882 by Jigoro Kano. Its most prominent feature is its competitive element, where the object is to either throw or takedown one's opponent to the ground, immobilize or otherwise subdue one's opponent with a grappling maneuver, or force an...

 as developed by Kano Jigoro

Kano Jigoro

was the founder of judo. Judo was the first Japanese martial art to gain widespread international recognition, and the first to become an official Olympic sport. Pedagogical innovations attributed to Kanō include the use of black and white belts, and the introduction of dan ranking to show the...

. It belongs to the fourth group of the traditional throwing list in the Gokyo no waza of the Kodokan

Kodokan

, or the Kodokan Institute, is the headquarters of the worldwide judo community. Literally, kō means "to lecture" or "to spread information," dō means "the way," and kan is "a public building or hall," together translating roughly as "a place for the study or promotion of the way." The Kodokan was...

 Judo.
It is also part of the current 67 Throws of Kodokan Judo.
It is classified as a side sacrifice technique

Judo technique

This page is a list of judo techniques. There are a variety of techniques recognized by Kodokan judo and other budō . Below is a partial list, organized by technique type and alphabetically within type....

 (yoko-sutemi).

Technique description

with the tani-otoshi you place your leg behind both legs of your opponent while still holding him in you favorite komi kata and pulling the opponent backwards resulting in your opponent falling on his back and you falling sideways.

Clinched Yoko-sutemi

In the video,
Gracie_Jiu-Jitsu_Basics_Vol.1,
Rorion Gracie

Rorion Gracie

Rorion Gracie is a Brazilian Jiu-Jitsu practitioner and instructor, a prominent member of the Gracie family, and a founder of the Ultimate Fighting Championship. He is the oldest son of Hélio Gracie and one of the few people in the world to hold a 9th degree red belt in Brazilian Jiu-Jitsu,...

 and Royce Gracie

Royce Gracie

Royce Gracie is a Brazilian professional mixed martial artist, a UFC Hall of Famer and Brazilian Jiu-Jitsu practitioner. A legend and pioneer in the sport of mixed martial arts, he is widely considered to be the most influential figure in the history of modern MMA.Gracie gained fame for his...

 demonstrate the
clinch

Clinch fighting

Clinch fighting is the part of stand-up fighting where the combatants are grappling in a clinch, typically using clinch holds. Clinching the opponent can be used to eliminate the opponent's effective usage of some kicks, punches, and mêlée weapons...

to foil a striker's game and
take him to the ground.
The animation below shows the use of a Yoko-sutemi technique
for the takedown.