Priority or right of way is the decision criterion used in foil and sabre fencing to determine which fencer receives the touch, or point, when both fencers land a hit within the same short time-frame (less than 1 second). After this window, if one fencer had already landed a hit, the electrical scoring apparatus would "lock-out," or fail to record, an opponent's subsequent hit, and thus the one fencer to land a hit is awarded the touch. In épée fencing, if both fencers land valid hits at the same time, they each receive a point. Because of this, foil and saber are considered conventional weapons. After a halt, a referee parses what happened into actions, from which it can be determined whether to award a point or not.
Offensive Actions
Offensive actions
Attack - An attempt to hit when the opponent is not already attacking.
Riposte - An attempt to hit the opponent after a successful parry
Counter-Riposte - An attempt to hit the opponent after a riposte was successfully parried
Counter-attacks
Counter Attack - An attempt to hit when the opponent is already attacking.
Other Offensive Actions
Redouble/Remise/Reprise - A second attempt to hit after a previous attempt missed or was parried Redouble - an attempt to hit which follows the original attack Remise - an attempt to hit which follows the original attack, without withdrawing the arm, Reprise - a new attack executed immediately after a return to the on-guard position.
Defensive Actions
The parry is the defensive action made with the weapon to prevent an offensive action arriving.
Point in line
The point in line position is a specific position in which the fencer's sword arm is kept straight and the point of his weapon continually threatens his opponent's valid target, which gains right-of-way.
Attacks on the blade
A fencer can 'beat' their opponent's blade as a preparation to make an offensive action (as opposed to hitting their blade as a parry to defend against an opponent's action).
Action Priority
An attack has priority over a counter-attack
A riposte has priority over a redouble/remise/reprise
An attack made with a beat has priority over an attack made without a beat
If both fencers make an attack at the same time then neither action has priority and it is considered simultaneous A point in line has priority over an offensive action if it was in place before that action started
Interpretation of Priority
Despite the simplicity of the underlying principles, priority rules are somewhat convoluted, and their interpretation is a source of much acrimony. Much of this acrimony is centered on the definition of attack. According to the FIE rules, an attack is defined as "the initial offensive action made by extending the arm and continuously threatening the opponent's target...". This is explained in the USFA Fencing Officials Commission FAQ: Initial refers to which fencer starts the action before their opponent does. Offensive indicates moving towards the opponent. Extending indicates that the weapon arm is moving away from the body - right of way does not require a fully extended arm. Continuously indicates that there is no "break" in the attack in which the attacker stops moving forward or holds back their arm. Threatening indicates that the attacker is in advance-lunge distance and close enough to hit, and their weapon's point (for foil) or blade (for sabre) are approaching the opponent's valid target.
The general consensus is that a useful guide is for the referee to look for which fencer's arm starts straightening first. In practice, referees, especially inexperienced ones, may go for the easy option and give priority to whichever fencer happened to be moving forwards. This is technically wrong, but it is far from unusual. There is also a school of thought, subscribed to by a relatively small minority, that priority should be given to the fencer who was the first to straighten their arm fully. This, again, is out of line with the current rules. The adherents argue that this is the more classical way of doing things, but this claim is dubious, as actual practice decades ago based right of way on which fencer started straightening the arm (not which fencer completed the extension); and the reworded rules conform better to actual, traditional practice which was documented in some older editions of the rules.