In many TaeKwon-Do patterns you punch with a side kick.
If this is so then why not punch with every kick:whip:
DArnold,
lol, sir, I love the naive approach you use as you throw out questions like this (just like you mentioned in your PM to me - - I'm sorry, I couldn't resist - you suckered me in! lol). I can just see the glossy eyed, innocent look on your face as you asked this question, followed by the gentle smile of someone who is really enjoying this! (of course, you know I mean that with all sincerity, and utmost respect)
I have heard many instructors proclaim that this is because, "if you miss with the kick then you will hit your opponent with a punch"
As you know, DArnold, there is a difference between those "instructors" who learn from books, and those who really learn.
Interesting though, I have never heard it described as a "punch," but I suppose there are many different ways of doing things. From what I have been taught (and this is just my personal experience - so don't take it as gospel... not that anyone would), it is a backfist technique, and it is not intended to strike anything. Just as valid as the physics and mechanics of internal muscle stability through reaction force (muscles that push and pull against each other), the extended hand (along with its reactionary hand), used with a side kick is designed to stabilize the upper torso, making the thrust of a linear side kick more powerful as well as controlled.
In conjunction with Isaac Newton's third Law of Reaction Force, the physical motion of the two arms moving in opposite directions around the torso (just like the reaction hand of a basic punch) creates opposing forces like that of a spinning top where the momentum of the object forces out equally in all directions creating centrifugal tendencies that counter each other, thus stabilizing the spinning which prevents it from falling down. Of course, "reaction force" is a natural part of all motion that we can neither avoid, nor turn on and off, but there are extensions of the use of reactionary forces through physical application, and scientific principles of technique.
In other words, reaction forces are occurring multiple times, on various scales, simultaneously in every movement of your body. For a good example of total body usage of internal reaction force, consider a cat that is held upside down and dropped. The unique twisting and torquing of the cats internal structure allows it to flip over in mid air without touching any outside object, and land on its feet.
In addition to internal reactionary forces, any impact between two objects creates another phase of reaction force when an applied force, or striking force is met with an equal and opposite return of reaction force (a ball hits a wall, it doesn't just drop straight to the ground). This reaction force is a repulsion and detraction of the applied force, working to spoil, or counter the striking force, but proper stability, stance, support, and even intentional reactionary movements of the torso and both arms can help to reinforce the technique, preventing the escape and dissipation of the reaction force.
This, of course, is not the only way to do the Taekwondo side kick, as many experts know that the initial fighting kicks in street combat are done with the guards held up, and not extended to expose the chest as they are in forms. Forms practice is designed (in the Taekwondo curriculum) not for a hidden meaning of self defense and secret codes, but to practice an early stage of technical training which employs the more powerful finishing moves.
While we can adapt, and modify these applications for variations of grabbing an opponent's body, blocking other attacks, or striking while kicking, there is no hidden meaning in the Taekwondo Poomsae by specific intent of their creators. It is a side kick, with a reactionary motion of a backfist extended over the leg, and the opposite hand drawn to the hip. Placing the other hand in a guard position is one option for combat, but it is not the move being practiced in Taekwondo Taegeuk (or Palgwe for that matter). Self defense applications of grabbing, or secondary hand strikes are optional add-ons with intermediate and advanced training.