Ikkyo Ura (aikido)
Uke attacks Nage with one hand/arm/weapon. Nage enters stepping with the foot matching the side of the attack, deeply but very slightly to the outside of uke's attacking arm and then pivots (tenkan) on that foot, bringing the trailing foot swinging around away from uke 180 to eventually plant the spot immediately behind uke's position at the start of the attack.
As nage takes the first entering step, his hands raise up together smoothly intercepting the arc of the attack at nage's elbow and wrist. Smoothly, at the time of contact, nage will gently overhand grab uke's forearm wrist with the thumb and forefinger of the hand opposite from the nage's attack, sliding down to bring nage's palm to the back of uke's hand down close to nage's hara. Smoothly, nage will hook his thumb inside the elbow joint of uke's attacking arm.
Nage first raises uke's elbow up slightly, and then pushes forward and down in an arc, turning uke's arm like a crank around the axis of uke's wrist (nage's hara), as nage turns tenkan. When the arm cranking motion bring's uke's elbow down to nage's hara, nage will then raise uke's hand, levering uke's body down at the fulcrum of uke's elbow. The form and posture of an effective pin should already be in force before uke strikes the floor with his free hand (or face).
When nage has completed the tenkan turn, he may pin uke by putting his knee down on the ground in uke's armpit. Uke's arm should be outstretched, but bent at the elbow slightly so that the elbow can be rolled forward similar to the earlier cranking motion. Uke's hand should be held to the ground above his shoulder or on top of nage's other knee if nage wishes to kneel. Nage applies pressure with the grasp on uke's metacarpals to uke's wrist by pointing uke's flanges toward uke's ear. Uke will have zero grasp strength, and may be easily disarmed.