Crab-Walking is a term coined by Gears of War players for a glitch that allows you to permanently roadie run. They call it Crab-Walking because of the funny way the character runs and strafes at the same time. The glitch is severely frowned upon by the Gears of War community and usually results in bad player reviews, complaints, and general trash talk around the match.
Crab-Walking is a glitch because it exploits the games change in animation from changing walls to a swat turn. The reason you are able to do this is because of the games internal lag. When you are host you are not able to do this glitch because it is running off your connection so there is no lag to allow you to do the glitch. The glitch allows you to roadie run (sprint) while still being able to fire a gun. There are almost no limitations, you are still able to aim and use any weapon you want. You are still free to pick up weapons and ammo. The only thing you are not allowed to do is press the A or B button. These cancel out the glitch and you will return to your original state. The advantage to using this cheat is just the sheer speed you obtain.
To do the glitch, all you need to do is memorize a simple button combination, its one of the easiest glitches in the game. Approach a wall that is next to another wall with a gap in between. It needs to be a small enough gap between the walls to let you slide from wall to wall. You can slide from any side of the wall, but for the purpose of this explanation you will start on the left wall. Now that you have found a spot, press A and put your back to the wall. Position your character at the end of the wall and hold right on the left control stick so the change wall icon appears. Once the icon is on you can perform the maneuver. What you want to do is change from holding right on the left stick to holding down on the left thumb stick. It is a very quick change. All you have to do is slide it around the edge until it gets to the bottom. Imagine a clock. You would be positioning it from 3 o’clock to 6 o’clock. Alright now that I have explained that to you, you also have to do another thing simultaneously. Probably a half of a second after you’ve slid the stick downwards you want to press A. Now it will take some practice on the timing, but eventually you will get it. Remember you can’t be host when doing this, and you can’t be playing on the hosts connection. The object of this is to basically trick the animation as if you were switching walls, but by switching the stick to the down position before you press A the character backs off the wall. Now if done correctly the character will shake a little and start roadie running. Make sure you hold down the entire time because the object is to back away from the walls you just used. If you come into close contact with the walls your character will be temporarily stuck to the wall and unable to move. Also if you get away from the walls you still shouldn’t return later on because you will get stuck. Now that you have backed away from the wall, you can sprint around and shoot at will. You will be much faster than your opponents and able to do everything they can do with the exception of rolling and using the B button. Essentially, you will be faster and more agile than your opponents, but you are not invincible by any means. Players can still kill you and they are usually trained to let you walk into them while their chainsaws are revved.