Spleef is a fairly common game to find on minigame servers. It is a large arena, with a floor made out of a material such as TNT or snow. Some have multiple floors; but all have a way of killing players who fall too far, either lava, the void, or simply a long drop. Players must break the blocks to send their opponents to their deaths.
TNT Bow Spleef - the floor(s) are made out of TNT. All players are equipped with a bow with Flame and Infinite enchantments. The aim is to shoot the TNT under the other player's feet, causing the TNT to ignite and fall, taking the target player with it.
Snow Spleef - the floor(s) are made out of snow, and the players will be equipped with (usually diamond) shovels, often with the Unbreaking X enchantment on it. Players attempt to break the snow under their opponent's feet.
TNT Spleef - very similar to TNT Bow spleef, but with no bows. This game takes advantage of the fact that TNT can be broken in one hit.