Preventing collusion created by tie-breaking rules

Games played in the last round of a round-robin tournament inspire match-fixing or tacit collusion if the two opposing teams can benefit from a particular result at the expense of other teams. In the case of four teams, the current study identifies all these situations caused by using head-to-head records as the primary tie-breaking principle. Simulations based on the 2016 UEFA European Football Championship reveal that the official tie-breaking policy substantially increases the risk of collusion, but it can be mitigated by choosing an optimal order of matches. Following the proposed schedule improves the competitiveness of the two games played in the last round and requires no reform on the format of the competition.