A comparison of incentive clauses of players contracts in German soccer and clauses used in the NFL and NBA shows considerable differences. Against the background of principle-agent theory we have a closer look at these incentive systems. In contrast to other industries it is easy to observe the employees, effort in team sports. Therefore, it would be desirable to set incentives for players based on their individual effort. We show that there are reasons why incentive clauses in professional German soccer, the NBA and the NFL are not directly based on effort. We argue that there are two main reasons: Firstly, efficient incentives are complementarily provided by subjective and objective performance measures. Secondly, cooperation amongst team members is essential in team sports.