Left 4 Dead 2 -

When a horde is triggered, find a corner or a wall to put your back against. This limits the angle from which zombies can attack.

Be extremely careful with frag rounds and explosives, as they cause significant splash damage to teammates. The Survivors and Special Infected left 4 dead 2

Swapping guns is faster than reloading. If you find extra weapons during a defense, use them to maintain fire without waiting for reload animations. When a horde is triggered, find a corner

To survive on higher difficulties like Advanced or Expert, teamwork is non-negotiable. When a horde is triggered