Yoko-shiho-gatame
(upper for quarter)
"The hold as it's name implies, is made from Uke's side.
Uke is lying on his back, you are face down on him, your two bodies
roughly making the letter "T". Your left arm is under
Uke's neck and gripping Uke's jacket at the left shoulder. While
your right arm passes under Uke's leg, the hand grasping Uke's
belt.
It is important that your right arm should pass between Uke's
legs high up in the crutch; otherwise Uke will be able to use
the full force of his thigh muscles against your arm, making it
impossible for you to hold on."