By now, you know the story. IOC threw eight players, in Badminton, out for “not using one’s best efforts to win.”
Did Michael Phelps give his best efforts during the semi-final? Did anyone, who had already qualified to advance but were not yet in the medal round?
In the book Freakonomics, the authors discovered that Sumo wrestlers who already qualified for next year’s promotion are likely to lose to an otherwise weaker competitor. In NFL, teams that have already missed the play-off have the incentive to lose to get a better drafting order, as well as a more favorable schedule for the next season.
For Badminton in this Olympics, the teams that have already qualified for the medal round would play for only one thing: the draw order. Since the championship round is a knock-out format, one loss and you are out. Everyone would like to avoid the strong teams until the last possible moment, preferably only during the medal round. Since the draw order is based on the win-lose record of the qualifying round, there is no incentive to win more after you have already qualified.
For any competition, or war, it is common to lose a battle to win the war. For Badminton, the strategy is simple: first try your best to qualify, then try not to win anymore. Those players were using their best efforts to win, just not necessarily for that specific match. IOC should throw out the Badminton World Federation, or at least their rule book.