Stonewall/Fallout 2

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

Fallout 2, Fallout Tactics, J.E. Sawyer's Fallout Role-Playing Game
Reduces the chance to be knocked down in combat. Since the chance is generally low and typically only occurs with purely melee foes, the perk is functionally useless.

Fallout: New Vegas
+5 to Damage Threshold against all Melee Weapons and Unarmed attacks. The player cannot be knocked down by any means in melee combat; explosives can still knock them down.

Bugs

 * The +5DT will be shown in the PIP-Boy menu whenever the player has a melee or unarmed (including no weapon) weapon equipped. However, the added DT will correctly only apply against melee or unarmed attacks, regardless of what you have equipped.

Behind the scenes
The early image used for this perk is a reference to The Thing, a member of the Marvel Comics superhero team The Fantastic Four.