Let's say hypothetically somebody has an apartment they aren't using and the lease isn't up until January. The Apartment has stated they will not all subleasing.

Would it be possible/legal to advertise that apartment for someone to stay at on Gamedays?

If the people staying there for 2 days are your guests then it is not a sublease. If your guests leave you an honorarium I don't think that is any of your apartment complex's business. You would just need to be picky about who you have as your guests because you will be liable for their behavior. How they treat the property, the neighbors, the staff will all impact if you get busted or not.

The question is how much risk are you willing to take on? If you are found to be in breach of your lease do you get evicted or get a slap on the wrist? The complex would rather have your rent then not have your rent.