Trigger Rush is a companion perk in Fallout 4.
Obtaining
To gain the perk, the Sole Survivor must be at maximum affinity with Cait, which is possible after completing her personal quest (Benign Intervention).
Effects
The official description in game is: The player character's Action Points regenerate +25% faster, if the Hit Points value is below 25% of its maximum.
However, this perk has never functioned this way. When the player character's Action Points are below 25 points, their action points actually regenerate 50% faster which makes this perk a good way to recover those first few action points much faster if one regularly runs out of action points (regardless of how much health.)
Notes
In the animation for this perk, Cait fires her pistol in time to the common Morse code signal "SOS".
