There are some issurim that one MIGHT be oiver from being a sports fan. If one avoids these pitfalls, I don’t see why it is ossur.
Issurim include:
Lo Sichonein= issur to compliment, flatter or to praise a non-jew. (this one is the toughest as a sports fan)
Nival peh= using bad language
(words in this catagory creeps into our subconscious minds when hearing how our “heros” speak. happened to me many times, I’m ashamed to admit.)
Negiya= this happens in crowded stadiums, and sports complexes, with people of the opposite gender sitting next to you, or when entering and leaving with the crowd.
these are the MOST common one can be oiver. yes there are more but it’s my personal list.