Combat tips

Rolling is important!

But did you know you can change direction while rolling? I always roll in and out to grab a chest on the edge of the map. You never know what is going to show up.
Also roll up and down to quickly reposition yourself for headshots rather than walking up and down.

You are also invulnerable while rolling so you can roll through attacking zombies to get easy headshots behind them rather than rolling around them.

Holding the fire button down while moving allows you to strafe. You will keep the direction you are facing while being able to move up and down, or backwards. Good for laying down a blanket of fire across the map or moving away from attacks while firing. No need to change direction to walk balk and turn around to fire.