Yul-guk on TMAC
At the blue belt level, the student practitioner has gained a nice level of technical proficiency. Basic Taekwondo techniques are coming together, sparring skills are accelerating, and the practitioner has a good perspective of most of the curriculum of the system.
So why introduce a technique like a jumping backfist in X-stance, like you see in Steps 35-26 of Taekwondo pattern Yul-guk? Ever knocked a person out with a technique like this? It's perhaps used as a gap closing technique - like a jab. You backfist someone straight into the face region and then close in with some other striking technique with back hand or back foot. The alternative for the backfist is to distract and then perform a spinning backfist which gains much more power. But this is not a spinning sportive technique.
From Karate, we see a similar technique in the opening sequence of Basai. According to a karate researcher, Basai is used as a technique against multiple opponents in the extraction of a principal or to inflict maximum damage against a larger group. The opening sequence could be an escape from some wrist or clothing grab. The next move is a jump into X stance and backfist. My hypothesis for Basai is that the jump X-stance is a body slam combined with a footstomp, and later a knee strike. The result is that attention is drawn to the backfist, allowing the practitioner to destroy the opponent's foot with the break and perhaps knockdown with elbow or backfist. (If the practitioner is surrounded, it would be difficult to see what his legs are up to.) The net effect is shock and awe that a smallish technique (the light back fist) sends that opponent directly into the ground.
The next thing I'd extract from Basai are feints and finger/joint breaks to opponents on all sides - who have just witnessed the jump/backfist move. Extreme mind-rocking stuff.
So we return to the Taekwondo blue belt. We do not need to equip him with any more fluff. Light techniques to be used in sparring can be acquired at his level through further solo practice, observing other opponents, and experimentation. The skills are this stage should prompt him to think about the opponent as a person - with human fallacies, who will react to pain and mind games. Deception. Distraction. Destruction.
See Yul-gok Step 36 as Take down for an additional interpretation of this move.
Yul-guk: If you Control the Head, You Control Him
Do-san: Backfists of Fury
Taekwondo Side Kick: Won-hyo v Yul-guk
Taekwondo Yul-guk: Neck Manipulation, Leg Defence, and Backfist
Traditional Taekwondo Technique Workshop