Upon receiving damage, increases the unit's speed for the duration of battle.The Ivalice Chronicles' description
Speed Surge, also known as Adrenaline Rush and Speed Save, is a reaction ability in Final Fantasy Tactics, learned by the archer job. It provides a chance to increase the user's own speed stat upon taking damage from any sources. The reaction ability must be learned by expending JP earned for the archer job.
Obtained
Speed Surge costs 900 JP to be spent on the archer job. Once the unit has learned it, they can equip it in their reaction ability slot to use it.
If a unit that knows Speed Surge becomes a crystal, a human unit picking up the crystal may learn Speed Surge without spending JP, as long as said unit has unlocked the archer job.
Mechanics
Speed Surge has a chance to increase the user's speed when taking any kind of damage from another unit, up to a maximum of 50 speed. The effect lasts the duration of the battle and resets once the fight is over.
Like the vast majority of reaction abilities, Speed Surge's activation is based off the unit's bravery; the higher the stat, the higher the activation chance.
Use
Speed Surge provides the unit with a small, yet incremental increase in their speed that plays a huge role in combat. With speed being one of the most important stats in the game, units can get turns earlier than the opponents, especially when paired with Haste. This can be particularly useful on frontline jobs such knights and monks, which are expected to take damage while approaching enemies, but have low innate speed.
Speed Surge synergizes with the archer's Aim, which requires a charge to activate and is directly affected by the speed stat. It is also effective for certain jobs that rely on speed for the success rate of their abilities, such as thief's Steal, machinist's Aimed Shot, and dragoon's Jump.