Sponsorship money is one of the sources of income for a Hattrick team.
How much sponsorship money a team will receive depends on the mood of the team's sponsors, the size of fan club and the league level it's in. The mood of the sponsors is influenced by two factors: how well the team fares in competitive matches and, much more importantly, the amount of spokespeople working for the team. The mood of sponsors is much less prone to fluctuations than supporter mood.
Sponsors are happier and pay your club more money if they have spokespersons they can talk/listen to. Research in the newbie (English) forum suggests that optimal number of spokespersons is around 1 per 250 fans. But it might be useful to temporarily hire more than optimal at the start of the season to recover sponsor mood quicker from the reset. Beware that more than 10 spokepersons will make your sponsors mood drop.