Conventions of combat - Rules of engagement

Definition

In SCA martial disciplines, we say combatants are "engaged" when they are allowed to strike each other.
You are not allowed to strike at an opponent if you are not engaged with them.
Scenario rules can define the specifics of "engagement", as long as they are clearly explained to all participants before combat begins.
Unless otherwise specified, the engagement rules listed below are the considered the standard.

In tournament single combat, you are engaged with your opponent at all times.
In tournament melee combat, you engage an individual opponent by moving into their line of sight and stating loudly, "Fighter - I am engaging you," or words to that effect.
In battles, you engage your opponent by moving into range in clear sight of the opponent you wish to engage and adopting an attacking posture. If you have reason to believe that your opponent has not seen you approach, you should state loudly, "Fighter - I am engaging you," or words to that effect.
You are not allowed to strike at an opponent if you are not engaged with them.
If you are engaged with an opponent and you turn your back on them, your opponent is allowed to strike at you until you leave weapons range.

Unit engagement happens when two or more cohesive units of two or more opposing combatants meet in combat.
Units can be of unequal size, or even consist of one person.
If you are in a unit, you are considered to be engaged with all the combatants who are part of the other unit(s).
If the unit you are fighting against loses cohesion, those combatants have stopped being a unit and must be engaged as individuals, as per the Individual engagement rules, unless they reform a unit of two or more combatants.
If your unit wraps around another unit, this means you may end up behind your opponents. As you are still engaged with the unit, you may strike opponents from behind and be struck by opponents from behind.

If you are using a ranged weapon, you are considered engaged with all other combatants on the field subject to relevant minimum range requirements.
Missile blows can strike from any angle and regardless of your awareness of the ranged weapon combatant or siege engine.
If you are using a handheld weapon, you engage ranged weapons combatants, as if they were any other combatant on the field.
If the scenario prohibits ranged weapons combatants from specifically targeting the back side of an opponent:
1. If you deliberately turn your back to avoid missiles, and a missile strikes you in the back, it is still valid.

The following standards may not be altered.
1. You must stay clear of moving parts.
2. You must not strike or thrust siege engines/structures with handheld weapons.
3. A siege engine that is considered destroyed must be secured/made safe.
4. If fighting occurs within 5 feet (1.5 m) of an active siege engine (cocked or loaded), a hold must be called and the engine declared destroyed and secured/made safe.
When possible, approach siege engines/structures from the side.
You destroy a siege engine by closing to within 5 feet (1.5 m) of the engine/structure and declaring “this weapon is destroyed.”
In the event that a Siege engine crew has been killed or captured, but the engine or structure itself has not been destroyed, the engine or structure may continue to be used by the capturing army.
Siege engine crews are fully armored combatants, and you should treat them as any other fighter on the field.

Kingdoms can choose to allow combatants to kill opponents from behind in battle scenarios by using the "death from behind" maneuver.
If your opponent is not engaged with you, striking them from behind is always forbidden. This standard must not be altered.
You must not deliberately ignore an attacker behind you, or repeatedly maneuver to keep your back to an attacker (thereby preventing an attack on you).
If you are not allowed to use the "death from behind" maneuver, or you cannot safely execute the maneuver, you must move to engage them as an individual or unit.
If a fighter is engaged with you, even though you are allowed to strike them from behind, the death from behind maneuver is preferred (if allowed).

Killing an opponent from behind can be accomplished by placing a weapon over your opponent's eye slot (or, for a two handed weapon or spear, upon their shoulder so that the point would be visible to your opponent) and stating loudly, "You are dead from behind".
If you are an archer:
1. the hand you use to perform the kill must have full hand protection which also protects your fingers and thumb.
2. you can use an arrow or bolt, but not your bow or crossbow.
You need to repeat this maneuver for every opponent to be killed in this manner.
You must take enough time that your opponent acknowledges your presence (or could have) before attacking another opponent (roughly 2-3 seconds).
You may not do this maneuver while running past your opponent.
If you are being killed from behind:
1. you are presumed dead as soon as the process has started.
2. you cannot spin or turn to engage the fighter.

You must not deliberately strike a helpless opponent.
Depending on the scenario or tournament rules, you may be allowed to declare a helpless opponent dead, ask them to yield, or allow them to regain the ability to continue safely.
If you get an unfair advantage by repeatedly becoming "helpless" (for example, by falling down or losing your weapon), the marshals will warn you, and if you do it again, they will force you to yield the fight. However, your opponent can ask the marshals to let the fight continue.