With a swift and deadly strike, a skilled warrior can cleave through armour.
If a model with this special rule rolls a natural 6 when making a roll To Wound for an attack made in combat, it has struck a ‘Cleaving Blow’. Enemy models whose troop type is ‘regular infantry’, ‘heavy infantry’, ‘light cavalry’, ‘heavy cavalry’ or ‘war beasts’ are not permitted an armour or Regeneration save against a Cleaving Blow (Ward saves can be attempted as normal).
Note that if an attack wounds automatically, this special rule cannot be used.