"Equips a back shield that provides protection against an attack from behind including melee attacks."
— In-game description.
Rearguard is a trait for the Phantom combat rig in Call of Duty: Infinite Warfare. It appears as a small shield equipped to the player's back and able to absorb a small amount of damage from enemy fire, or melee attack, before it is destroyed. A new shield will protect the player when they re-spawn.