  The non-scientific event of a soccer match is analysed on a strictly
scientific level. The analysis is based on the recently introduced concept of a
team fitness (Eur. Phys. J. B 67, 445, 2009) and requires the use of
finite-size scaling. A uniquely defined function is derived which
quantitatively predicts the expected average outcome of a soccer match in terms
of the fitness of both teams. It is checked whether temporary fitness
fluctuations of a team hamper the predictability of a soccer match.
  To a very good approximation scoring goals during a match can be
characterized as independent Poissonian processes with pre-determined
expectation values. Minor correlations give rise to an increase of the number
of draws. The non-Poissonian overall goal distribution is just a consequence of
the fitness distribution among different teams. The limits of predictability of
soccer matches are quantified. Our model-free classification of the underlying
ingredients determining the outcome of soccer matches can be generalized to
different types of sports events.
