I don't think it's stupidity. I mean I don't understand it. At all. But it's ultimately just another fandom which stems to passion. And I can understand at least that.
More like obsessive passion, which to me is stupidity... People beating each other up just because someone hurled an insult about the other side's "team", riots in the streets and smashing other people's properties just because "their" team lost...
Anyone that resorts to violence when their own or people they love lives are not at stake is stupid in my book.
For example, I am passionate about Fallout games but I would never start throwing punches at someone that tells me that Fallout 4 is the best and that old fallout games are shit
.
I would point out why
I think they are wrong and if that failed probably use some sarcasm as humour to lighten the mood and that would be it.
And yes, there are plenty of sports fans that do not become violent, but those can still become depressed and/or stressed about it or let the game have a too big influence over their lives.
On a different note, even some of those that are not violent will become violent if they are in a big group that starts smashing stuff or beating up people, mob mentality makes people do stuff they would never do by themselves and not being able to control or think by yourself in those situations is being stupid too.
So what I am trying to say is that being passionate about anything is good, but being obsessed or letting stuff you enjoy shape your daily life is not good but stupid. And
the average sports fan seem to be included in the stupid category, I said average because there are still plenty that are not like that, the sports fans category is huge and pretty much involves people in every country and region and area in the entire world so of course that even not being in the average category still leaves many people left
.