Also you should note that you get more for killing zombies than killing humans. This is becuase the point of the game is to not be a zombie. The structure of the ranking assumes that you tag 3 humans every time you are a zombie as a base. Also it assumes that if you are a zombie and die it is very bad. You never lose points from being taged by a zombie but you do lose points when you die.
The ranking for a good player assumes:
They kill a lot of zombies
They do not get taged
If they are a zombie they tag a large number of humans
They never die