America has plenty of other religions that aren't classified as religions - sports (as you have pointed out), but also partisanship and politics, work, addictions, money, fame, influence, etc. All of these things offer what religion does - meaning and purpose, a sense of belonging, special language, giving your money over in offering, sacraments (those things that allow us to feel the divine - in sports it might be a ball from the game), priests to proclaim the message, holy documents, and some even offer origin stories too.