Fight Or Flight is a movement gear perk that speeds you up after you take damage. It helps you run for cover the moment a fight turns against you.
Getting hit gives you a short burst of speed. Use it to break line of sight and reach cover before the next volley lands.
One of the more reliable speed perks for the feet slot, since you will take damage in nearly every fight.
No Time to Spare starts health regen sooner, so you recover quickly once you reach cover.