What is the ruling on participating in a league where each player pays a certain amount to his team, knowing that the prizes are not monetary but rather a cup and medals?

Competitions that involve financial compensation (betting) are a form of prohibited gambling (maysir), which Allah Almighty has associated with wine, idolatrous altars (ansab), and divining arrows (azlam). It is not permissible to take compensation in a competition except for horses, camels, and arrows, due to the Prophet's (peace be upon him) saying: "There is no prize (sabaq) except for an arrow (nasil), a hoof (hafir), or a camel's foot (khuff)," and because these are instruments of war that one is commanded to learn.