Lockout gravity lift trick
From Halopedia, the Halo wiki
The colloquially-termed "Lockout gravity lift trick" is a trick on the multiplayer map Lockout of Halo 2. It may surprise an enemy in pursuit. Go up to the top floor of the grav lift. If you jump right down the hole at the very front ( closest to center area) The Grav lift will work in reverse, rapidly propelling you down the shaft.