Similar to Press Advantage, this special effect forces the target to make an Opposed Test of their Willpower against the attacker’s hit roll. Failure means that the target hunkers down behind whatever cover is available, and cannot return fire on their next Turn. Note that Pin Down works even if no actual damage is inflicted on the target (perhaps due to a successful evasion or shots striking their cover instead), as it relies on the intimidation effect of projectiles passing very close by.
Although a pinned victim is unable to fire back for the requisite time, they can perform other actions provided they don’t expose themselves to fire in the process, such as crawling away to new cover, communicating with others, reloading a weapon, and so on.