Crouching is a general mechanic that has recently appeared in the Resident Evil series, and has so far only appeared in three games.
This page is not for crouching as a situation or contextual maneuvers such as in Resident Evil 6.
In Revelations 2, Press B or Circle for Crouch.
Resident Evil: Revelations 2
Starting in Resident Evil: Revelations 2, the ability to crouch has appeared as a part of the general gameplay mechanics, which allows the player to sneak around certain enemies, albeit at the cost of speed when doing so. Crouching is mapped to a designated input and can be used freely. In Resident Evil: Revelations 2, there are specific abilities that can boost the player's character when they do crouch, such as Crouch Power, Crouch Dodge and Crouch Advantage, the latter of the three being available in the campaign.
Resident Evil: Umbrella Corps
In Resident Evil: Umbrella Corps crouching can be used to shorten the hitboxes of the player character, and even allows the player to move at a speed almost identical to the base running speed.
Resident Evil 7: Biohazard
Crouching returns again in Resident Evil 7: Biohazard. Crouching is, once again, a slow stealth mechanic that also functions as a way for Ethan and other playable characters to move around in crawlspaces scattered around the game, and move underneath some objects. Crouching is also very useful for dodging certain attacks from enemies and bosses, and is even part of an achievement in the game.
The crouching speed in this game can be buffed by equipping the Walking Shoes.