According to Daniel May members wear armor spanning the ages from the 6th century to the 16th. This also means the shields span the same period. To keep it even, the rules for the fights are that a thrust to the face would kill a combatant in real life. So regardless of helmet, every body is assumed to wear open faced helmets. To avoid real injuries there are protective devises on the helmets.
People are also assumed to be wearing chain mail, since a glancing blow “could kill or break bones.” There are safety monitors to keep everybody safe. It is fun, and it is also a good workout.