public void abortWarmUp(Player player)
   {
      if(null != player)
      {
         if(playersOnWarmup.containsKey(player.getName()))
         {
            // check if warm-up is still running for this player
            if(null != playersOnWarmup.get(player.getName()))
            {
               // cancel players warm-up task (which is still running) to prevent task stacking
               playersOnWarmup.get(player.getName()).cancel();
            }

            playersOnWarmup.remove(player.getName());

            if(player.isOnline())
            {
               player.sendMessage(ChatColor.RED + "Abgebrochen");
            }
         }
      }
   }