I am trying to model the number a goals scored by the teams of a soccer tournament at group stage. The tournament involves eight groups of four teams each. This means that each group involves 6 games and therefore there is a total frequency of 96 determined a priori. However there is an observed over-dispersion. Poisson distribution fit hypothesis is therefore dropped in preference for a negative binomial fit hypothesis. My problem is how to compute the expected frequencies under the negative binomial fit. I need assistance.