  If the final position of a team is already secured independently of the
outcomes of the remaining games in a round-robin tournament, it might play with
little enthusiasm. This is detrimental to attendance and can inspire collusion
and match-fixing. We demonstrate that tie-breaking rules might affect the
occurrence of such a situation. Its probability is quantified via simulations
for the four groups of the 2022/23 UEFA Nations League A under two
well-established tie-breaking rules, goal difference and head-to-head records.
In these home-away round-robin contests with four teams and 12 matches, the
competitiveness of the final four games can be promoted by giving priority to
goal difference, which reduces the chance of a fixed position in the group
ranking by at least two and usually five percentage points in the last round.
Our findings, supported by sensitivity analysis in a theoretical model, provide
important lessons on how to design ranking systems.
