How can this happen in America? In Beaver Falls? Just outside Pittsburgh/ sarcasm
Last night I was at a comedy act in Duesseldorf when the funny comedian announced that he had a confession to make. He said "I'm from Cologne." Suddenly the entire audience erupted in loud boos, 800 people in unison.
He set himself up for that.
His act was a big hit with the crowd, by the way.
In the USA, anyone who wears a competing city's football jersey, especially at a propitious time, has to expect a major healthy reaction. Healthy means no violence. But...after that, for instance, the local restaurant can invoke their "no shirt, no service rule" and refuse service...as long as it is clear that the protagonist knows it is meant humorously and he won't go hungry (proximity of other restaurants, etc). Otherwise, it wouldn't be funny anymore.
And it wouldn't be classy for home city fans to be that way when a large number of "enemy fans" happen to be in your city for a game. The "punishment" for being an "enemy fan" would have to be a lot less in that case, it it were to remain funny.