To start I'd like to alleviate your fears if you are sent a notification from a referee you'll have time to remedy any violations they may state. It would also require that at least 4 of the referees all agreed you were doing a bad activity so I hope that helps calm some of your fears.

I'm not sure how to address all of the activities that you mentioned because I'm not familiar with them all but I would imagine that some would be ok. Other activities like food contests might be shaky as they may not deal with sports so that may violate a guideline.

Farming rewards is intended towards users who are violate the concept of proof of brain through schemes like self upvoting multiple comments of your own. This is done in hopes of gaining additional rewards from both author and curator side of the post rewards. This isn't the only example of such behaviors but is one of the intentions behind its use.