The figure-4 can also be used as an arm lock. It's basic and effective. I'll first describe the "vanilla" version I learnt first during learning jiu jitsu.
- Standing about 1.5 ft to the lockee's, uke's, victim's or whatever-you-want-to-call-them's right side 90 degrees from each other, take their right wrist in your right hand. The wrist is held in the same orientation as if you were shaking hands, but obviously you're further up the arm.
- Slide your left foot closer to the uke's right foot
- Simultaneously stretch your left arm across the uke's throat or chin as a distraction and stretch your right arm so their right arm is extended. This is like an exaggerated early morning yawn-and-arm-stretch.
- Once fully extended, bend your left arm and bring it under the uke's right arm, under their elbow. Grasp your right forearm firmly with your left hand, knuckles upwards.
- Their elbow should now be being pushed the wrong way by your arms in a T-shape, the inside of their forearm uppermost. If you aren't in this position, you grasped their wrist wrongly. It’s in a roughly “4" looking shape, which is where the name obviously comes from.
This practice version can be turned into some neat-o moves, and here are a few faves:
- This technique is best used for backfist type strikes. After blocking a backfist with a double forearm block, grasp the wrist with the closer arm, and then apply the lock.
- It can be done facing the uke, with their right elbow being pushed upwards using your left arm from below, your left arm holding your right forearm, with your right hand on their right shoulder, for support. Use this version to "get them on their toes”, then turn in with your right shoulder to their right armpit for a shoulder throw/ippon seoinage.
- After applying the lock, relax the pressure a little, slide your left foot in an arc, allow them to bend their arm back but then apply a shionage throw, with optional leg sweep. This throw, for those that don't know the term, means four directional throw, and involves folding the arm back to the shoulder and beyond, so the body is thrown off balance. It’s a basic aikido technique.
- It's a good ground move too.
PLEASE don’t muck around with this kind of thing - it’s a potentially damaging hold. If you want to learn this kind of stuff go to a judo, jiu jitsu, aikido or wrestling etc. class. It’s good fun, I assure you.