There's this system of using towers or something - I'm not sure what it's called - but each tower can sense something within its range, making sort of an imaginary circle. If two towers sense something and their circles intersect, it's there.

That's basically the system I used here, with command blocks using the [r=5] thing, and if any entity is within its range, a redstone lamp will turn on.

There will be an invisible player or mob, and they will try to shoot all the other players who are trying to shoot them as well. 

The catch is that the redstone lamps sense arrows too, being entities, so the more arrows, the more lit redstone lamps. 

A way to make all the arrows disappear is to shoot a button outside the arena, but it will expose your back to the enemy.

If you forget these rules, you can always check - there's a button at the spawn.

There's two modes: Players vs. Player and Players vs. Mob.


Yeah, I didn't really test either much; just tell me any problems!

EDIT: This map will likely never be finished, or at least close to never. On my computer, at least, there's way too much lag to do anything. I may continue this on a smaller scale, if at all.