They didn’t come up with the sports team example, it comes from the comment they are responding to.
Hey, you can do a real-world test to see if I'm right or you are right. Go to a football match (soccer for Americans), find a group of hooligans and tell them their team sucks. If you are right and it's just petty entertainment - you'll be just fine.
However, you should acquaint yourself with the principle of subsidiarity. Loyalty, duty, and love radiate outward from those who are owed the most diminishing to those who are owed the least (spouses, then children, then parents, etc., all the way through extended family and then community and nation and finally the human race). The loyalty is to the objective good. How that is expressed will be modified by contingent factors particular to a given person's situation.