'Choose Your Opponent': A New Knockout Format for Sports Tournaments. Application to the Round of 16 of the UEFA Champions League and to Maximizing the Number of Home Games During the UEFA Euro 2020

Abstract

We present a new knockout format for sports tournaments, that we call "choose your opponent", where the teams that have performed best during a preliminary group stage can choose their opponents during the subsequent knockout stage. The main benefit of this format is that it makes the group stage more exciting, by giving teams a strong incentive to perform at their best level. It also makes the group stage more fair, by limiting the risk of collusion, canceling the risk of tanking, and making sure that the best group winners are fairly rewarded. Advancing teams would choose their opponent during new, much anticipated TV shows which would attract a lot of media attention. We illustrate how this new format would work for the round of 16 of the UEFA Champions League, the most popular soccer club competition in the world. This format can also be adapted to maximize some objective. For instance, we show how it could have been used to maximize the number of home games during the knockout stage of the UEFA Euro 2020, the first edition of the soccer European championship to be hosted by 12 countries.

Keywords: sports, tournament design, fairness, choose your opponent, knockout, UEFA, Champions League, Euro 2020