Just say hypothetically, you are offered a job in some kind of admin/media/finance role at your main rival's football club by a friend of a friend.
You've been referred and the employer's very interested. They'll give you a rise on your current wage of about 5%.
The only qualms are - you have to wear the emblem and colours of the club in some way every day (either on your tie or a badge or something).
Do you take the job? And if so, do you let your new employer know about your loyalties?