Grim Reaper's Sprint

Grim Reaper's Sprint is a perk in Fallout 3, Fallout: New Vegas, Fallout 4, and Fallout: The Board Game.

Effects
Landing a killing blow in V.A.T.S. will immediately restore all Action Points, allowing the beginning of a new series of attacks immediately. However, foes killed by allies (or other means) will not trigger the perk, even while in V.A.T.S.

Effects
In Fallout: New Vegas, the perk only gives back 20 AP on a kill in V.A.T.S. Although this is a significant reduction to the effectiveness of the perk, the perk is still very useful with high power, low AP cost weapons. The effectiveness of Grim Reaper's Sprint is dependent upon three things: AP cost of the weapon, damage of the weapon, and toughness of the enemy.

Be aware that the perk restores 20 Action Points if an enemy is killed in V.A.T.S., not per enemy killed; e.g. killing 3 weakened enemies in a single round of V.A.T.S. will only restore 20 AP, not 60.

The following perks and traits complement Grim Reaper's Sprint: Fast Shot, Kamikaze, Action Boy/Action Girl, Math Wrath, and Better Criticals.

Effects
When fully maxed out, this perk can be incredibly useful in the mid to late game, particularly in large battles. This is because higher level enemies are often accompanied by lower level "cannon fodder" types, who can be instantly killed at higher levels. These enemies essentially provide a reasonably reliable source of regaining Action Points, since at higher levels they can usually be killed in one or two shots, with a 35% (at max level) chance of activating Grim Reaper's Sprint.

Fallout: The Board Game
When Grim Reaper Sprint is discarded, the player character gets one additional action after each fight where they kill an enemy, until the end of their turn.

Behind the scenes
Grim Reaper's Sprint was a fan-created perk and winner of the Fallout 10th anniversary perk contest in 2007, submitted by Marc-Andre Deslongchamps. Bethesda implemented the perk in Fallout 3, describing the idea as "elegant and simple" while affecting game mechanics in a unique way.

Bugs

 * Sometimes upon taking this perk, it will not restore AP. Instead, it just takes up a perk slot that could have otherwise been used on something else.
 * APs gained through gear in Fallout 4 will not restore. (a total of 195 APs, 30 APs through ultralight mod, Grim Reaper fills APs up to 165.)