Minecraft wiki entry for Spleef, associated text: Creating blocks between the game's start and end is forbidden.
Creating or destroying blocks after you have lost the round is not allowed.
The losers must replace the blocks that were deleted during the game after the round is over. (Optional, occasionally a script or commands/command blocks are used instead)
If players have entered a stalemate and are all on separate "islands," and unable to access each other to continue to play, either the person with the most space wins, or the arena is reset to continue play. Usually, the latter happens only in arenas that use a script to reset the play field.
Hitting players is against the rules, except in variations.