Armor lock

Armor Lock is an armor ability in Halo: Reach and is only available to Spartans.

Description
When performing an Armor Lock, the player is invulnerable to all damage, but it also renders the player immobile. Along with this, when the Armor Lock is activated, it will shed stuck Plasma Grenades and Needler rounds. It will emit a slight Electromagnetic Pulse when in use. The animation for Armor Lock is a Spartan, slamming his fist on the ground. In doing so, he starts to emit an EMP as long as the button is held or until the Armor Lock ability is over. Armor Lock will also drain the shields of an opponent foolish enough to attempt a melee attack.

Armor Lock can be charged up in three stages, with each stage inflicting a stronger EMP and pushing opponents farther away. Armor Lock does restore health or shields unless someone attacks you while in armor lock. It also provides a few moments of invincibility, while making you immobile. The ability will recharge once you stop using it. A quick way to neutralize the advantage of a Spartan using armor-lock ability is to remain outside the EMP zone, fire one shot at him every once and a while to keep his shields down and then attack when he's done.