Step 19 of Toi-Gye is not a guarding block. It is officially a "low double forearm pushing block". This motion is weird for a few reasons:
- The only other kind of "pushing block" is the palm pushing block, which like its name suggests to meant to push the opponent with the palm.
- This movement appears in no other ITF patterns. It is unique to Toi-Gye.
- Despite the stated purpose of a "pushing block" being to push the opponent off balance, the only application we ever see for this motion is blocking a kick.
- Similar motions used to push down an opponent -- such as the low knifehand guarding block -- are usually open-handed. Why the closed fists? And why is the inner-forearm used to block?
I wanted to see where this movement came from. In General Choi's 1965 book Taekwon-Do: The Art of Self-Defense, he lists instructions for several karate kata in addition to the original 20 ITF patterns. The low forearm pushing block appears in two kata: step 10 of Gankaku (which Gen. Choi calls "Ro-Hai" for some reason) and steps 10 and 27 of Tekki Sandan. I looked up youtube performances of the patterns and compared the "pushing blocks".
|(Left) Low forearm "pushing blocks" from Toi Gye (left), Genkaku (Middle), and Tekki Sandan (Right). Source: Shotokan Sensei|
Neither of these motions look like Toi-Gye. In Genkaku the outer-forearm is used. In Tekki-Sandan the inner-forearm is used, but it's in riding stance and the position of the back arm differs. So as far as I can tell, the motion is unique to Toi-Gye.
Here I suggest that the use of the name "pushing block" is literal. I know it's common for bunkai researchers to say that the name of the block means nothing, but when a unique motion is used with a unique name, I think we can make an exception
Specifically, we use the pushing block to create a rear wrist lock, a police hold that appears in the Encyclopedia of Taekwon-Do (Volume 5, page 313). We follow with a knee strike to the opponent's lowered head, and then a throw via a head crank.
We begin with the counter-clockwise turning W-block (mountain block), using it to create an armbar.
Notice how the tori lands his front leg in front of his opponent's right leg. This is important: we are setting up a trip. The armbar should be a forceful one, utilizing the 180-degree swing we perform in the pattern. This will knock the opponent's shoulder forwards.
As you step in with your left leg, bend your opponent's arm such that their elbow is up, as in a hammerlock. Now you will switch hand positions: grab their left knifehand with your right hand. As you maneuver your arm into the low inner-forearm block, you will naturally curl your opponent's hand and bend their fingers in towards their inner elbow. Make sure to bend their arm behind their back, and grab their elbow with your right hand for control. This creates the rear wrist lock.
|(Left) How the low inner-forearm block turns the opponent's wrist. You may bend their fingers towards their elbow. (Right) The rear wrist lock, although the grip in this case is different. Source: Bertoni Defense Systems|
Bending the opponent's wrist in causes them to reflexively bend forwards, so you can use both fists to literally push them forwards and to the ground. The direction of the wrist actually pushes them down to the right (towards their elbow), and so when combined with the trip they may fall onto one knee.
If they don't fall, follow the pattern: grab the back of their head with both hands and knee strike their face. Then grab the head with both palms (left hand underneath, right hand on top) and crank it as you turn around into the knifehand guarding block , attempting to flip and throw the opponent by their head.
A wrist lock application might seem too esoteric for some, but this is application that both (1) follows the pattern and (2) explains why it is called a "pushing block". This lock also appears in the Encyclopedia of Taekwon-Do, so I'm not pulling it out of nowhere.
 A head crank is a common application for the knifehand guarding block. If you move your two palms closer together, then moving from the setup to the block-proper mimicks grabbing and cranking the head.