I'm guessing you're from the UK? This isn't specific to teams. Any group is referred to in the plural in the UK and the singular in the US. For example, "the police is" vs "the police are".
The City Council is … The class is … The police are … The firefighters are …
The phrase "the police is" sounds so foreign to me, that I am almost certain I've never heard nor said it.
I hadn't noticed the wider use of singular groups previously, but that does make sense when you point it out. I suppose it was just more obvious because we rarely see american analysis of football outside of the world cup.