Shotgun Rush is a gear perk that gives you a burst of speed after a shotgun kill. It helps you push from one enemy to the next in close-quarters fights.
After you kill an enemy with a shotgun, you move faster for a short time. Use it to close the gap on the next target before they can react.
Wear the Clown Feet in the feet slot. Gear perks are fixed to the piece of clothing that carries them, so you get this one by wearing that piece, not by unlocking it in a menu.
Shell Pocket keeps you stocked, and Rampage can make your shots free after a melee kill.