Certainly people can see why one needs to move in a martial art, but there is quite a bit more to it than chasing the bad guy. Jujutsu is a positional fighting system. This means that the tools you have available to you depend on where you are in relation to your opponent. Can you punch someone standing behind you? How about to your side? Actually you can briefly disarm your opponent simply by body movement (no this isn't a long-term solution). For a smaller, weaker person this can completely determine success or loss. Another thought has to do with the influence of sports. really if you are more or less equal to your opponent, you can exchange blows. This makes great sport, but the assumption is that striking is rendered safer since there is no disparity of force. Even more crucial is when there are weapons involved and exchanging blows is immediately fatal.
We advocate initally having very deep stances, i.e. having your center as close to the ground as you can. This does two things, the first is merely practical in that it builds up your legs to work through their full range of motion. Most people walk using only a fairly small range of motion with their legs and hips. Once this is exceeded, strength falls off drastically. Since you will be moving people in a variety of ways, we don't want you to suddenly lose power in the middle of a technique. There is a safety issue here, since the most likely way for novice to get hurt learning a throw is to lose stability/strength in the middle of a technique and fall.
Secondly, we are a grappling style and the distance between opponents is usually less than a handspan (on the order of 6 - 8 inches or about 15 - 20 cm). Changing the horizontal distance is not usually much of an issue at this point, but making sure your center of gravity is lower than you opponent's is critical. Stances are actually designed for very close in grappling work where you must change your relative positions quickly while having maintaining stability with a potentially much large opponent hanging on to you.
A linear force is relatively easy to counter, but once that involves
a curved path is quite likely to disrupt balance. Therefore being able
to generate force while being
stable in motion is very desireable. Dropping or raising your center of
gravity as needed is a quick and effective way of countering any
off-balances from your opponent. Generally though, as speed increases,
stability drops off.
In practice, you will start from a normal walking position in most techniques, but once engaged you will doubtless endup in a variety of positions. We will cover the following basic techniques.
We will also start several drills for stability.
Finally, we have several footwork drills
The taisabaki used are
Advancing (through the center) - Moving directly towards an opponent in such a way as to remove his ability to root. This is the purest form of entering. The basic idea with entering is essentially jamming his whole body. Two bodies cannot occupy the same space at the same time, so as the attacker moves, if you occupy where he intends to go, he cannot complete his movement and will automatically be off balance.
Crowding - moving close to an opponent to rob him of movement. To move, the attacker must have space. If you are too close you effectively smother his weapons.
Dropping/Lifting- lower or raise the center of gravity.
Evading - movement laterally to avoid attack.
Leading - moving ahead of the opponent so as to force him to follow you.
Retreating - moving straight back from an opponent to avoid attack. This must be done in such a way as to avoid being in a disadvantageous position! Tip: shuffling (really a quick hop) is better than walking if you must retreat. You should offline as soon as possible (pivoting is fast).
Sticking - maintaining body contact with an opponent. This goes well with crowding, but is not a synonym. You should be matching speed with you opponent at all times since he then (relative to you) slows down.
Turning - reaction of the body to a push so as to retain alignment and root. This might just be a twist into kosa dachi or a full body movement.
Twisting - rotating an opponent off his root, such as by turning his shoulders. Notice that this refers to the opponent, not you.
Walking - yes, walking, but along a curve so that balance and control are emphasized.