If you were sent an account credit, you will receive it right away and will be able to use it immediately.
If you are being refunded to your credit card/original payment method, you will receive a message in your OpenSports chat from the OpenSports Help Desk (or through email, if you have a web account). The actual refund will come 5–10 business days after receiving this message.
Note: You will have to check your own bank account to monitor when you actually receive the refund.
Note: This answer relates to events (pickup/drop-in games, practices, multi-week classes, trainings and camps). This answer does NOT relate to league or tournament registrations.