  Many sports tournaments are organised in a hybrid design consisting of a
round-robin group stage followed by a knock-out phase. The traditional seeding
regime aims to create balanced groups roughly at the same competition level but
may result in several uneven matches when the quality of the teams varies
greatly. Our paper is the first challenging this classical solution through the
example of the men's EHF (European Handball Federation) Champions League, the
most prestigious men's handball club competition in Europe, which has used
unbalanced groups between the 2015/16 and 2019/20 seasons. Its particular
design is compared to an alternative format with equally strong groups, as well
as to the previous scheme of the EHF Champions League. We find that it is
possible to increase the quality of all matches played together with raising
the uncertainty of outcome, essentially without sacrificing fairness. Our
results have useful implications for the governing bodies of major sports.
