The relative importance of ability, luck and motivation in team sports: a Bayesian model of performance in the English Rugby Premiership.

Results in contact sports like Rugby are mainly interpreted in terms of the ability and/or luck of teams. But this neglects the important role of the motivation of players, reflected in the effort exerted in the game. Here we present a Bayesian hierarchical model to infer the main features that explain score differences in rugby matches of the English Premiership Rugby 2020/2021 season. The main result is that, indeed, effort (seen as a ratio between the number of tries and the scoring kick attempts) is highly relevant to explain outcomes in those matches.