Proof

In some recreation groups, the combat rules specify that certain pieces of armour are not vulnerable to certain weapons. For instance, in the SCA, plate armour is sometimes treated as arrow-proof, so a fighter wearing such armour is not "killed" or "injured" if the armour is hit by an arrow. However, other weapons (e.g. swords, cannonballs) are still effective. Depending on the group, these rules may be the norm, customary or one-offs for that particular war.