Make sure you're in a fight with more than one enemy and your health is extremely low (10-20). Activate Berserker just before you enter Fight For Your Life! Mode, then kill someone to gain a Second Wind. If done properly, you should be able to run as fast as Brick can in Berserker mode AND you'll be able to fire your weapons. Note: you're not able to sprint while using this, but why would you need to anyway? Activating his Berserker mode again and finishing it, OR dying will cancel the effect.