Stonewall (Fallout: New Vegas)

 is a Fallout 2, Fallout: New Vegas, Fallout Tactics and J.E. Sawyer's Fallout Role-Playing Game Perk.

You are much less likely to be knocked down in combat.

Fallout: New Vegas
You gain +5 to your Damage Threshold against all Melee Weapons and Unarmed attacks, and you cannot be knocked down by any means in combat.
 * This perk is bugged. It will actually give you +5 DT as long as you are using a melee or unarmed weapon, not the attacker. The DT bonus is valid for all forms of damage.

Behind the scenes
The picture used is a reference to one of the Fantastic Four members; The Thing.