From Armagetron Advanced Wiki
In Armagetron, a player may bind more than one key to a turn direction. For example, binding two keys for a left turn, and then pressing them both simitaniously will result in a quick one-eighty turn-around. Double-binding has a long and glorious history smattered with a fair bit of controversy along the way.
The earliest known double binder is Locutus. His reasoning was that since he had a bit of carpal tunnel syndrome, it was easier to play the game if he bound two or more keys to the same actions. So when he started doing it, it was to deal with a condition that might otherwise be considered disabling. You know, kinda like having one of those doughnut pillows to drive.
From there, it started spreading to younger more able-bodied individuals who wanted to exploit it to get the other guy. On the older servers, it wasn't a large problem because if you turned around too quickly against a wall, your cycle bounced.
After a certain period of time, another player by the name of Digital Logic popularized the phrase "Double binding is a crutch of the weak", talked a bunch of trash on the forums, and then ran away when the inevitable challenge came. We had the tournament anyway, it was a lot of fun. Here's the original thread
180s in 0.2.7.1
The double-edged sword that is Armagetron Advanced 0.2.7.1 had a fix for the bounce bug. It also had some refactoring of rubber code. The end result was that it was now possible for all players to turn around quickly against any given wall many times in a row. The double-binding crowd jumped all over it and created a situation many older players considered almost unbearable.
In addition to double binding, players can also bind as many times as they want which leads to triple binding which is great for making "knots".
Armagetron works using complex numbers. On the standard grid, when you turn, your direction is multiplied with i or –i. You must step aside some distance to turn around. A recent approach uses j and k offered by quaternions to literally get around it. Instead of stepping into i, you would step into one of the other imaginary dimensions. However, you would leave the grid in the process, precluding others from hitting your walls.
A slightly more fruitful and mathematically sensible approach is negative binding, which makes you double back into your own wall. Understandably, it's still not the paragon multi-complex-binders are looking for, although it appears to be the limit of their ideal as sidestep distance goes to zero. Possibly, this confused ideal is related to the misunderstanding of quaternions. Indeed, quaternions might have been picked because it was thought nobody (at least within their clique) would be able to understand the flaws. Investigation is ongoing.