A gauntlet is a metal glove that is designed to protect the hand and wrist during combat. It could be an articulated metal mitten or glove. Mail gauntlets attached to the sleeves of a hauberk are known as mufflers. The first gauntlets (likely of leather reinforced with whalebone) appear after 1290 but are very rare. Steel gauntlets are also mentioned in the last 5 years of the 13th century.
Gauntlets in the SCA
In the SCA, all fighters must wear hand protection as part of their armour. For heavy fighters, this ideally is a gauntlet, but sometimes the cheaper option is a sporting glove like a gumby. The exception is if the hand is already protected by something else, e.g. something covering the handle of a shield. Archers can wear a light glove with the tips of their draw fingers being uncovered. Fencers must wear at least a glove. Armoured gloves are treated as a different piece of armour and have special rules regarding their use.
Gauntlets in Re-Enactment
Gauntlets in re-enactment are typically of the same style as would have been worn by actual warriors. Generally a combatant may not enter the field without some form of hand protection but the degree of protection varies with time period and group as well as type of combat that the combatant will be undertaking. In generally the more likely the person will be struck on the hands the more likely that a substantial gauntlet will be required.