Ferocious Loyalty

 is a perk in Fallout: New Vegas.

Effects
The power of your personality inspires die-hard loyalty from your followers. When you drop below 50% health, your companions temporarily gain much greater resistance to damage.

The resistance to damage gained from this perk does not increase your companions DT. The resistance applies to the damage your companions receive after your companions DT has been subtracted from the damage taken. On average the damage taken by your companions will be reduced by 75%, the exact formula is currently unknown.

The increase in resistance is not really temporary. Ferocious Loyalty will continue to stay active as long as your health is below 50%.