“Your martial might is truly legendary. You do a large amount of additional damage through enemy blocks with all Melee Weapons and Unarmed attacks.”— In-game description
Unstoppable Force is a perk in Fallout: New Vegas.
Effects
More specifically, this perk multiplies the player character's Melee and Unarmed damage by 4 when striking a blocking opponent, which allows for serious damage to be inflicted in spite of the additional Damage Threshold provided by their blocking.
