Damage Shields are pools of additional health that take damage before Health is reduced. There are two types of shields: Bullet Shields and Spirit Shields, each of which blocks only the respective damage types. Melee Damage is also blocked by bullet shields. Damage Resistances do not apply to shields. Once damaged or fully depleted, they will fully recover after some time.
Any instance of excess damage dealt to completely destroy a shield is then done to health.
For example, a Dynamo with 100 spirit shield health takes 168 spirit damage from Vindicta's Assassinate. 100 spirit damage will break Dynamo's spirit shield, the remaining 68 spirit damage is subject to spirit resist, and the final calculation is done to health.
Recovery
If not fully depleted, a shield will begin recovery if it has not been damaged in the past 20 seconds. This countdown will be interrupted by taking damage.
If fully depleted, a shield will begin recovery after 50 seconds regardless of whether the player has taken the respective damage type recently. This recovery will persist for a few seconds even after the player has taken damage.