You may choose to sacrifice yourself in order to protect another.
Prerequisites
Benefit
On your action, you may choose to subtract a number from your Armor Class and add that same number to an ally’s AC. The number you subtract from your AC may not exceed your base attack bonus, and the ally must be within your melee reach. The penalty on armor class applies until the start of your next turn. The bonus to your ally’s armor class applies until the start of your next turn or until the ally is outside of your melee reach.