Heresypedia

Particularly cruel or deadly weapons sometimes include things like living barbs or shards that remain in their victims’ wounds causing them immense pain and even slowly killing them. When a target suffers at least one wound from a weapon with the Crippling (X) quality, they count as being “crippled” for the remainder of the encounter or until healed of all Damage. If a crippled character takes more than a Half Action on their turn, they suffer Rending Damage equal to the number in parenthesis (X). This Damage is not reduced by armour or Toughness.