Well it's all about the elixer-infected-players. There have been more post about it, like this one. It seems private games are the only solution, unless you want to boot all elixer-infected-players. Be sure to see the difference between a 5 min daily and 30min+. Ever since elixers are payable by gold and not just platinum this has been going on.

But you can use this rule, elixer-infected or not: if a lv 61 player has less then 35.000 kills, they are no good. Certified.