If you've ever played Halo: Reach or Halo 4, you've probably played the gamemode "Grifball." This is a recreation of that gamemode in Minecraft. The goal is to place TNT on the opposing team's redstone block to detonate their base. You can set your own score limit. Includes team selection, armour and weapon droppers, and a start lever.
Extract the .zip and put the folder in your "saves" folder of .minecraft.