Melee

Melee is the act of physically attacking an enemy by hitting them with a weapon or an arm. In the Halo series, the majority of melee attacks involve using a ranged weapon as a bludgeon, while there are a few weapons that are melee-only. By default, a melee attack can be executed by pressing the B button on the Xbox/Xbox 360 version of Halo: Combat Evolved, Halo 2, Halo 3, and Halo 3: ODST,by pressing the F key on the PC version of Halo: Combat Evolved and Halo 2, or by pressing the RB button on Halo: Reach.

Overview
Melee attacks are stealthy and conserve ammunition. The close-range attack causes damage to the target's bones and tissues, allowing an attacker to injure a target without expending ammunition. A melee from behind functions by breaking the target's neck or spine, and is sufficient to kill almost any enemy in the games, regardless of how much shielding or armor they happen to be wearing. Also, one melee against a sleeping Unggoy, regardless of difficulty or their rank, will kill them instantly.

In Halo: Reach, a new melee gameplay mechanic, called an assassination, is presented. Holding the melee button while behind the target will result in a complex animation viewed from a third person viewpoint, ranging from stabbing the opponent to breaking necks.

In Campaign, melees are classified as "silent", thus, meleeing an enemy will not alert any other enemies who have not already noticed you. However, assassinations are not "silent' and will alert nearby enemies.

Melee attacks are commonly used in multiplayer matches, where only a few blows are needed to kill an opponent; they allow one player to kill another without the sound of gunfire revealing their location or the weapons they are carrying.

Occasionally, two players with depleted or near-depleted shields will hit each other at around the same time, resulting in both players dying simultaneously. While rare, this can be annoying.

Lunging
When a player melees, it is possible to lunge forward at an enemy who may be some distance away.

For melee weapons, when a target is close enough that an attacker's reticule turns red, the attacker can press RT and lunge forward towards the enemy to get in range before striking. The lunge distance for the Energy Sword is considerably longer than that of the Gravity Hammer.

Lunging is also possible without a melee weapon, however the enemy must be very close to the player, as the lunge distance is much less than that of a melee weapon. This also applies if a player is using B to attack with a melee weapon, instead of RT.

Halo 2
Halo 2 's melee system was based on three levels of player movement, with a stationary melee doing the least damage, a running melee taking down roughly half of the target's shields, and a jumping melee almost completely removing the target's shields.This does not apply to multiplayer. With the introduction of dual-wielding, a new feature was added: if a player performs a melee attack while dual-wielding, they will drop their left weapon.

In Halo 2, melee attacks had the added benefit of canceling various animations and delays. This trait was shared by various other actions, and was exploited in the form of special button combinations. A common combination is the Double Melee, a rapid repetition of the button sequence B + X.

The range of the melee attack was decreased in Halo 2 from Halo: Combat Evolved, but the distance at which a lunge can be attempted was increased.

Halo 3
In Halo 3, the attack's power increased, such that two blows to a normally-shielded opponent's body were sufficient to kill them. The attack also became more effective against some Campaign enemies, with fewer hits required to kill a Flood Combat Form. A Halo 3 title update balanced melees; if two unshielded players melee each other, both will die, and both will receive a point.

The increased power of Halo 3's melee attack has led to various new tactics and techniques regarding its usage. A common tactic is to charge an opponent using an Assault Rifle; the attacker drains their opponent's shields with the rifle, and then uses a melee to finish them off. Melees are also used in Noob Combos, with a common combo being the usage of a Mauler to drain an opponent's shields, followed by a melee.

A new feature is the ability to perform a normal melee attack while using melee weapons. Such weapons have both an RT attack and a B attack. The Energy Sword's B attack is a rapid swipe that is faster but with a reduced lunge range; The Gravity Hammer's B attack is a jab with the butt of the hammer. This does the same amount of damage as a regular melee attack with a ranged weapon, but does not expend any battery units.

Assassinating an opponent in multiplayer earns the player an Assassin Medal, while a normal melee kill yields a Beat Down Medal.

Halo 3: ODST
In Halo 3: ODST, the power of the melee attack has been drastically reduced, because the player characters, ODSTs, are ordinary humans, much weaker than the playable SPARTAN-IIs and Elites from previous titles. Although attacking from the rear is still lethal, it can take several hits from other angles to take down even the lowly Jackal, and trying to take on a Brute in hand-to-hand combat is risky, though 3-4 hits on normal difficulty is still lethal. However, it's still possible to board a tank and destroy it with a few melees, likely for gameplay. If you use Brute weapons to melee however, you would get a much higher damage rate because of the blades attached to the weapon.

Halo: Reach
In Halo: Reach, one melee attack completely depletes shields, but cannot "spill over" and do damage to health in multiplayer unless the players shields are already down. Additionally, a new melee gameplay mechanic is added, Assassinations. Holding the melee button while behind the target will result in a complex animation viewed from a third person viewpoint, ranging from stabbing the opponent to breaking necks. Unfortunately the downsides of assassinations are that they leave a player vulnerable and take a relatively long time. While performing as assassination, other players can kill the opponent you are assassinating, stealing your kill, or kill you, saving your victim. However, assassination will give you an Assassination Medal, additional credits and advance the Rear Admiral (commendation). Additionally, if you are falling from a high height, performing an assassination on an opponent on the ground will negate any fall damage you would have received. There are more than 40 different animations that change depending on the species assassinating or being assassinated, as well as the position of the players, and the weapon used.

Trivia

 * In Halo: Combat Evolved, a melee attack in the back can kill a Marine instantly. However, this is changed in Halo 2 and Halo 3.
 * If a player gets too close, Hunters will use their shields as melee weapons. A common tactic in Halo: Combat Evolved was to get close to a Hunter, then duck behind them while they swing to get an unobstructed shot at the weak point on their back. In Halo 2, Hunters were given rearward attacks specifically to counter this tactic.
 * Another effective tactic was to shoot the Hunter in its unprotected waist area when it melees. With a sniper, shotgun, or (in Halo 1) M6D pistol, the Hunter could be killed in 1 shot. Hunters have extra armor from Halo 3 onwards specifically to render this tactic useless. In addition, sniper shots are also no longer guaranteed kills.
 * In Halo 2 's campaign, one melee from a Elite on Normal difficulty can instantly kill the player, Rarely, the player doesn't die; the player should not have taken any damage, and the melee was delivered in the front.
 * In the pre-beta (Bungie employees and staff only) versions of Halo 3 Multiplayer, the melee was less powerful, with a single melee failing to significantly deplete a player's shields.
 * In the Halo 3 Campaign, the Arbiter can melee while dual-wielding Plasma Rifles without dropping them. Similarly, Brute Chieftains who carry Plasma Cannons can still melee the player with it, most likely due to their colossal strength. The player, who takes control of a Spartan-II, the Arbiter, or Elites in Campaign and multiplayer canonically has the strength needed to peform such feats, however allowing this would affect game balance.
 * In Halo 3, it is possible to assassinate a player through thin glass, such as that found in the bases on Valhalla and Snowbound. Also, a melee on the right shoulder will grant an Assassination Medal, the left shoulder will not.
 * In Halo Wars, the Spartans will often "drop" their weapon to start meleeing a close enemy.
 * If the player melees during the right time in Halo: Reach when an enemy lunges with the energy sword, the player can survive. However, the damage performed leaves behind very little health and the sword wielder can lunge a second time, killing you. However, it is possible that gives you enough time to flee or kill the sword wielder.
 * In Halo: Reach, the Energy Sword does not consume it's energy when an assassination is performed. The sword specific assassination will also display even if the sword is out of energy.
 * Marines can melee in Halo 2, but the attack is weak, and is only seen when the marine is sneaking up on an unaware enemy. Their melee attacks aren't enough to kill most enemies even from behind.
 * The description of a melee attack in Halo: Reach from Bungie.net is "Not The Face!" This is a quote from Red Vs Blue, specifically by Griff who said it while he was getting punched.