In the core rules shields provide a fixed amount of protection, and helmets are figured into the protection armor provides. This is a bit simplistic, and is replaced with the rules below. Helmets Their primary funktion is to provide extra amour to a vunerable area, the head. It provides its damage-reduction die to all hits. […]
Tied Criticals cause each combatant 1d3 points of damage, bypassing armor, to represent buffeting and general fatigue. This rule does not apply during non-lethal combat. Tied criticals on a joust (lethal and non-lethal alike) hurl both lancers to the ground for 1d6 damage each and shatter both lances.