During gameplay, a player has the physical option to commit suicide. While this isn't the objective of the game, and doesn't benefit the player in any way, it is a regular occurrence during the games.
During gameplay, the player can commit suicide in several ways. The player can kill himself/herself by the use of their own weapons. An example being standing near a self thrown grenade, or firing a Rocket launcher at the player's feet or nearby wall.
Another method, is to crouch down and stick yourself with a Plasma Grenade or a Brute Spike Grenade. If done quickly, you can run or jump in the midst of enemies or players killing them and yourself. Comparable to a Kamikaze Grunt.
A second method would involve less effort. The player could encounter a group of enemies and allow themselves to be killed. This method isn't technically suicide, as the player doesn't kill himself/herself, but does cause it. This, like any other death, causes the player to restart from the last checkpoint. This may also lose a player points if they are on the Halo 3 Meta-game.
An advanced suicide method is possible on a metal floor, where the player can crouch, and shoot Needler rounds at their own foot (However, there is no super detonation). If done correctly, the player can eventually commit a successful suicide, as the needler rounds bounce off the floor into the player's foot.
One last method is to stand next to a stationary energy barrier wielding a non-energy weapon (e.g. Assault rifle, Shotgun.) Shooting the energy barrier while standing next to it will cause your shots to bounce back at you, harming you and, eventually, killing you.
Either during a system link, or online play on Xbox Live, the player can use the same methods as can be used during campaign. However, when a player commits suicide on multiplayer, the announcer will say "Suicide!"
Suicide during multiplayer loses a point for a player. You will also get a respawn penalty.In Halo Wars, causing a base to self-destruct can be seen as a method of suicide, same as using The Prophet of Regret's Cleansing Beam on your base or the Chieftain's Vortex ability, as Arbiter's power will not affect your own base.