SoalaIf you're crouched against a wall directly to your right or left, look at a slight angle horizontally away from the wall and hold your corresponding movement key against the wall awhile moving forward/back, you'll go faster than normal crouching.
Not a perfect example, but here's it being used.
https://www.youtube.com/watch?v=pwwgh__diFM
This is likely an artifact of wallstrafing, a quirk of the goldSrc engine. In goldSrc games you get a lot more speed (roughly 1.5x), and you don’t have to crouch. You can see it in at the beginning of the most recent half life run here.