  For every sports tournament, it is an important requirement to provide
contestants with the appropriate incentives to perform. However, incentive
compatibility is usually considered an all or nothing (binary) concept in the
academic literature, that is, the rules are proved to be either strategy-proof
or vulnerable to manipulation. Our paper aims to present a method for
quantifying the violation of this theoretical property through the example of
the European Qualifiers for the 2022 FIFA World Cup. Even though that
competition is known to be incentive incompatible since lower-ranked Nations
League group winners are interested in the success of their higher-ranked
peers, the extent of the problem has remained unexplored until now. Computer
simulations reveal that the threat of tanking can be substantially mitigated by
adding a carefully chosen set of draw restrictions, which offers a justifiable
and transparent solution to improve fairness. Sports governing bodies are
encouraged to take our findings into account.
