I'll ask the question again without mentioned football or basketball in the subject:
This may seem like an easy answer, but it could be set up several ways:
the Event organizors (whether it be NCAA, the Boston Marathon, Tour de France, NASCAR) find sponors for the event. Some of the sponsors agree to advertise during commercial breaks. The network charges the event organizors a flat fee and then additionally profits off of the advertisors.
The network takes care of finding the advertising, dipping into the events existing sponsors, and takes a portion of its profits and pays the event organizors a flat fee.
Anyone have any insight into how this taken care of?