Knockdown Weapon FusionTweet
(from Starfinder Core Rulebook)
With the knockdown fusion, a weapon disrupts a target’s center of gravity. The weapon gains the knockdown critical hit effect. If the weapon already has a critical hit effect, when you score a critical hit, you can apply either the weapon’s normal critical hit effect or the knockdown effect. Only weapons that deal bludgeoning damage can benefit from this fusion.