A guard is a physical defence against damage. For weapons this might include a crossguard for a sword or dagger, a rondel guard for a saw, ahlespiess or dagger or a more elaborate defense such as the basket hilts found on some rapiers or swords.
There are numerous variations on guards including swept hilts, proto mortuary, shell guards, bat wing and cup hilts. These guards are generally made of a softer steel or other metal due to their not needing to be of the same quality as the blade. Guards have been engraved for decoration at different times in history and others might have incised decorations or none at all.
The guard of a weapon does not always act in a defensive manner and Talhoffer (amongst others) indicates that it was also used offensively.
Weapon Guards in the SCA
Guards for weapons vary quite considerably. In order to avoid wearing gauntlets many in the SCA add a basket hilt-like guard to the backs of shields that sport enarmes and also to a number of weapons that would not normally have them (either due to nature of the weapon or the period).
Weapon Guards in Re-Enactment
By and large, re-enactors do not substitute basket hilted guards due to an understanding that they change a weapons balance considerably from the original. Thus they are usually essentially the same as historical guards.
Guarding may be a long term task (eg. in a prison) or a short term one (eg. "Guard my flank").
A guard is someone whose current primary task is to guard someone or thing. These range from a town guard to a royal guard. The Varangian Guard and Huscarls are well known period examples of the latter category.
Guards in the SCA
In Ealdormere it is traditional to have a ceremonial guard placed on the King and Queen. This guard, armed with live steel (although safely sheathed) protects the Royal Persons. In Court one or more guards stand at the edge of the Royal Presence. Standing as a ceremonial guard is considered an honour by some.
Interestingly enough, at one Australian event, guards were once set by one re-enactment group after a particularly unsuccessful SCA/re-enactor event. Many stories were created and subsequently embelished, and much soured the relations between many NSW re-enactors and SCAdians for years after the infamous Morisset (re-enactor's title for the event).
Other SCA guards