Unstoppable Force

 is a perk in Fallout: New Vegas.

Effects
"Your martial might is truly legendary. You do a large amount of additional damage through enemy blocks with all Melee Weapons and Unarmed attacks."

More specifically, this perk multiplies your Melee and Unarmed damage by 4 when you strike a blocking opponent, which allows you to inflict serious damage in spite of the additional Damage Threshold provided by their blocking.