Try this, without checking Corners:
-- Wait until both the players input something, or one leaves the game.
repeat task.wait() until not (DefendingPlayer and AttackingPlayer and Defender.Value and Attacker.Value) or ((AttackingPlayer.Backpack.Data.ChosenMove.Value ~= "") and (DefendingPlayer.Backpack.Data.ChosenMove.Value ~= ""))
-- Checks if player leaves the ring
local hasPlayers = DefendingPlayer and AttackingPlayer and Defender.Value and Attacker.Value