Floating shot glitch
From Halopedia, the Halo wiki
The floating shot glitch is a glitch in Halo: Reach. The glitch causes the fired shots and bolts from specific weapons such as the Spartan Laser and Plasma Launcher to remain floating above the ground and not injure the target.
To perform this glitch, start a Forge match with at least two players on separate teams. Have one player pick up a Plasma Launcher and have the other player stand still. Lock the Plasma Launcher on to the player and fire the bolts at them. Once the bolts stick, have the stuck player enter monitor mode. The bolts will stay floating in the air where they stuck to the player. They will not move or explode unless the stuck player leaves monitor mode. This glitch can be performed by a single player by creating a shield door or one-way shield and angling the shots to bounce off and stick the player.
For the Spartan Laser, charge it, but do not fire it. When it's about to fire, enter monitor mode. There should be a red dot floating where the Spartan Laser beam was charging. It will stay there until you return to player mode.
This glitch works with any Energy Weapons that require charging.