A hidden benefit of incomplete round-robin tournaments: Encouraging offensive play

Abstract: This paper aims to explore the impact of tournament design on the incentives of the contestants. We develop a simulation framework to quantify the potential gain and loss from attacking based on changes in the probability of reaching the critical ranking thresholds. The model is applied to investigate the 2024/25 UEFA Champions League reform. The novel incomplete round-robin league phase is found to create more powerful incentives for offensive play than the previous group stage, with an average increase of 119\% (58\%) regarding the first (second) prize. Our study provides the first demonstration that the tournament format itself can strongly influence team behaviour in sports.