Sankaku gatame video
Info about "Sankaku gatame video"
Sankaku gatame (triangle arm lock) is one of the official 29 grappling techniques of Kodokan Judo. It is one of the nine joint techniques of the Kansetsu waza list, one of the three grappling lists in Judo’s katame waza enumerating 29 grappling techniques. 
This hold starts from a possition similar to kami-shiho-gatame. Tori holds Uke’s head and right arm, forming a triangle with his legs. Tori’s bent left leg encircles Uke’s neck and arm. Tori’s left instep overlaps in the popliteal hollow of his right knee. Tori wraps his right arm under Uke’s waist and takes hold of Uke’s belt. 
From Wikipedia  and greenbankjudoclub.co.uk