Answer: The sporting event takes place.
Step-by-step explanation:
By the Revenue Recognition principle of Accrual based accounting, revenue is only to be recognized when it is earned. In other words, it should only be recognized if the service or good that was paid for has been delivered.
In the above scenario, the service to be delivered is the sporting event. As such, the event promoter should only recognize the revenue when the sporting event is delivered by taking place if they are going by the Revenue recognition principle which is a principle recognized by both U.S. GAAP and IFRS.