  The forecasting of sports events is of broad interest from the applied but
also from the theoretical perspective. In this work the question is addressed
for the example of the German soccer Bundesliga how a theoretically optimum
forecast of the goal difference of a match can be characterized. This involves
a careful analysis of the random contributions in a match and its
disentanglement from the informative contributions, resulting from the
individual team strengths. An important aspect is the consideration of the time
dependence of the team strength which turns out to mainly fluctuate around a
team-specific value during the course of a season. Two types of time-dependent
properties have to be distinguished, one being uncorrelated between different
match-days, the other being correlated and thus accessible by an appropriate
correlation analysis. For some performance indicators, which may be used to
estimate the team strength, the quality of the respective forecast is compared
to the theoretical optimum. Knowledge of the informative contribution allows
one to conclude that the offensive team strength is more important than the
defensive team strength for the final success.
