A Dumb defense to negate the first attack that strikes you. Can be provided by various game abilities or plot created scenarios. From the Accelerant core rules book:

"You negate the first attack of the appropriate type that strikes you. Although different verbals are used to indicate the nature of your defense and to add flavor to the game, this defense works in the same way as Elude and Shield. You must call out this defense when it is used."

The primary difference between this ability and an Avoid, Parry, or Resist is being required to expend the defense on the very first thing that hits you. You can't wait for the right opportunity to activate it, you must activate it immediately. If you were struck by a smaller attack, you would have to use up this defense. It is possible to use other abilities in place of this defense if it's appropriate so that you can use this defense during some other "first attack" in combat. From the Accelerant core rules:

"Although Guard defense must be used if an attack would affect you, it is possible, for example, to use a skill that provides a Resist defense when an appropriate attack strikes you to “protect” a Guard type defense. You could, for example, use a Resist against Fear to save a Guard against any Mental trait."