Note: the following is essentially a lift of an idea that Trollsmyth puts forth here, which I've swiped for my own purposes, with some tweaks and modifications.
During combat, a participant can forgo taking damage from a successful attack by sacrificing either a shield or a weapon, under the assumption that is was shattered while parrying/ deflecting an incoming attack.
The only caveat is that it must make a certain amount of sense for the defender's shield or weapon to be able to absorb the damage of the incoming attack. In practice, this generally means that the incoming attack must either be a blunt or cutting weapon (not counting daggers), as piercing attacks usually would not break an opposing weapon or shield. The defending item to be sacrificed can be either a shield, or pretty much any weapon except a dagger (not counting main-gauches, daggers just usually aren't used much as parrying weapons).
If being attacked by a big monster (one that has enough mass and STR to break a defending weapon) that is attacking with its natural limbs and/or claws, if a cutting weapon is sacrificed to deflect the incoming attack, said cutting weapon in this case also does half the weapon's base damage to the monster.