43. Choi-Yong W-shape block

Here's another weird one. In Choi-Yong we see an outward W-shape block performed with the knifehand. 

The full set is:

• Steps 21-22: Perform two palm pressing blocks in a fast motion
• Step 23: Turn 180-degrees into the W-shape block
• Step 24: Back leg front kick
• Step 25: Land backwards into a forearm guarding block OR (Step 28) land forwards turning 180-degrees into a forearm guarding block

If you interpret these movements as "blocks" you run into absurdities. So let's take a deeper look at what may be going on.

First we can use the two palm pressing blocks as an arm drag, demonstrated by karate culture in the image below. The first palm pressing block sets up the drag, then use the second block to pull the opponent's triceps (downward palm) while stepping forward.

Source: Karate Culture

This places you behind the opponent, so turn 180-degrees (like in the form) to get their back. Overhook their left arm (the one you dragged) with your left arm and reach around their neck with your right arm. Execute the W-shape block, stretching out your opponent's neck while tightly holding their arm.

Finding an image of this exact technique proved difficult, so try to fit the below two together:

Like the top image, we can overhook their left arm and place pressure on their rear shoulder. (This is sometimes called a "bar arm", distinct from an "arm bar".) And like the bottom image, we can push out the opponent's jaw with our right knifehand. In practice, substitute whatever rear control technique you feel comfortable with.

Next, front kick the opponent's groin. This could also be a knee strike to the tailbone. The first time we perform this technique, we land backwards into a forearm guarding block (Step 25). This is useful if the opponent's arm drops behind them. We hold their arm behind them with both fists, creating a hammerlock.

Source for left image: George Vranos

If the opponent is pulling their arm away from you, land forward and turn 180-degrees so you end up in a waki gatame lock, another application for the forearm guarding block. In the form we practice this while attacking the opponent's right arm. 

Following the form, we use a walk forward, turn and slide back to throw our opponent (Step 29). If they don't cooperate, the lock will hyperextend their elbow, breaking their arm.