app/models/play.rb

@@ -14,6 +14,7 @@ class Play < ActiveRecord::Base
   after_save :set_controlling_player
 
   def check_for_winner
+    return if self.game.winner.present?
     if self.game.over?
       self.game.winner_player_id = self.player.id
       self.game.status = "Player #{self.player.display_name} wins!"