Blocks physical attacks received from the front or side with the equipped weapon.The Ivalice Chronicles' description
Parry, also known as Weapon Guard, is a reaction ability in Final Fantasy Tactics, learned by the knight job. It grants the unit a chance equal to their equipped weapon's physical evasion stat to completely evade a physical attack from the front or sides. The reaction ability must be learned by expending JP earned for the knight job.
Obtained
Parry costs 200 JP to be spent on the knight job. Once the unit has learned it, they can equip it in their reaction ability slot to use it.
If a unit that knows Parry becomes a crystal, a human unit picking up the crystal may learn Parry without spending JP, as long as said unit has unlocked the knight job.
Mechanics
Parry grants the unit a chance equal to their equipped weapon's physical evasion stat to completely evade a physical attack from the front or sides. Parry is one of the only two reaction abilities not affected by the bravery stat, the other being the ninja's Reflexes.
If the job equipped with Parry is a ninja or another job with its Dual Wield support ability, each weapon grants an independent chance to evade.
Use
Parry provides an extra layer of protection to units in addition to the job's own physical evasion, equipped shield (through jobs that can equip or the knight's own Equip Shields support ability), and/or equipped cloak.
Parry works exceptionally well with certain weapons, such as the main gauche, the dancer's cloths and the defender, all which have very high evasion rates.
Parry is mostly useful in the early to mid game, but gets outclassed later by the samurai's Shirahadori, which does not rely on the equipped weapon, instead granting physical evasion based on the unit's bravery stat, potentially rendering them virtually invincible against most physical attacks.