Crusader Zombies are not much different than the normal Zombie, other than their spawn behavior and unique appearance. When they spawn naturally to attack a generator, they will only attack generators and will not attack players. The only time they will attack players is when you are trying to power a generator or when in The Crazy Place.

If they succeed in disabling a generator, they will move to the next powered generator and continue until all generators are disabled or until you have killed the group of Crusader Zombies. If you kill the group before they can disable any of the generators, you will be granted a Max Ammo Power-Up.