Ude-hijigi or Ude hishigi
(arm bracket or arm crush)

"This lock is attempted when both Tori and Uke are engaged in tachi-waza. An opening for it's application can occur if Uke carelessly stretches his right arm to his front. With your right hand grasp Uke's right wrist from the inner side so that the thumb side points towards his elbow. The inner side of his arm is kept upper most (your hand must be over his wrist). Advance your left foot a little and turn your body to the right so as to bring you round to his right side. Pin Uke's right upper arm under your left armpit. Your left under arm should be in close contact with Uke's elbow or it's upper part and should pass underneath so that with your left hand you can grasp your own right lower lapel. The role of your right hand gripping your opponents right wrist is to push the latter downwards in the reverse direction, forcing Uke to tilt foreward on his toes. As you keep up the downwards preasure on his right wrist Uke is unable to relax and severe pain is inflicted on his elbow joint."