You don't need to go to a football game to learn the rules. Just read Wikipedia.

I'd suggest that you just relax and ask questions when you get here. People will not expect you to know American "quirks and peeves".

Are you going to UI at Urbana or Chicago? I graduated from the Urbana campus.

As for local, indie things to do in NYC...the list is endless and even a lot of touristy things are still kind of local and indie. The truly indie stuff is not advertised. YOu just have to know people who are in the know. NYC is very much an insider's city. Check out gothamist.com for some local flavor.

The festival season is over. You can check out what bands are playing at small concert venues - but there are so many such venues! Fall foliage season will be in full swing at the beginning of your visit. YOu go up to Vermonth or New Hampshire, generally. But I bet you could take the Metro-North train to one of the more remote stops and see some nice colors.