Knockback
From FOnline: Aftertimes
Knockback is the ability that a weapon may have to knock your target down while at the same time pushing it over the ground, be it because of the perk of that name or the type of damage they inflict.
The following weapons have the Knockback perk, triggered by a critical hit only:
The following weapons can knock back your enemies due to their type of damage, triggered by any hit:
Shotguns (all types) can cause knockdowns up from 10 hexes. 10% per bullet chance to knockback.