Defensive Strike

Defensive Strike is a Void-element melee ability for the Sentinel subclass, part of the Code of the Protector tree. Killing an enemy with it creates an overshield around the Titan and nearby allies, shown as a blue bar over health.

The wiki lists the initial overshield duration as 10 seconds, though that figure is marked as uncertain. With Turn the Tide active, the overshield lasts up to 20 seconds and also increases melee damage and reload speed until it is destroyed.