This is in danger of running into the back/forth that we saw in the Angels and Airwaves Wikipedia page :-)
Joking aside, it might sound odd to an American (or Canadian?) but British English would not distinguish between whether or not the name or “nickname” are singular or plural. So we would say:
The Seahawks are winning
Seattle are winning
Arsenal are winning
Rangers were relegated
I think this is the kind of thing where you can learn to tolerate the “wrong” one but it’ll always sound weird to you, whether “wrong” for you is British or US English :-)
Edit: I did think of a situation where we’d use “is” - when you’re referring to the legal entity or FULL name of the club. “Aberdeen Football Club is a Scottish professional football club based in Aberdeen”. This is pretty rare to see, and you’ll likely just see it in, ironically enough, the first line of a Wikipedia page.
"The" and the postscripted "s" imply plurality, and therefore the use of "are". Nearly all sports teams in the US are pluralized, so it would be "the Seahawks", "the Bears" etc. There are a small handful of counter exactly examples, such as the Utah Jazz and the Miami Heat. But I think most sports fans use their standard sports lexicon that they use for every other team and treat team names as plurals.
Band names tend to be mixed. It's clearly "the Red Hot Chili Peppers are playing at..." but also "Primus is playing at...". (See also the edit war between "The Eagles" and just "Eagles")
I think the use of "The" as part of the name also matters.
"The Patriots are winning" sounds OK to me as an American. "The Patriots is winning" sounds totally wrong. "Arsenal are winning" sounds fine, "Arsenal is winning" also sounds fine.
When I think of American sports teams there's usually an understood "The" in front. "Patriots are winning" works fine conversationally but, if you were being a bit more formal or writing it down, you'd say "The Patriots are winning." On the other hand, the city name is singular. "Boston is winning."
Something that comprises many people is treated as singular unless it's in a plural form.
-Arsenal is a team.
-We are Arsenal players.
-There are many arsenals in Britain, but there is only one Arsenal.
If it's unclear you have to add words. You have to make sure the subject is singular. With Arsenal the singular nature of the word doesn't require it.
-There are many patriots in the USA, but there is only one Patriots football team.
In your example, Arsenal is the singular team. "Arsenal players are winning" is grammatically correct but not really used because players are understood to be part of a team.
The difference is that most U.S. sports teams names are proper nouns in the plural form (49ers, Raiders, etc.), but most motor sports teams are usually referred to as Team <Singlular Noun>. "Team Quaker State is in the lead." If they were the Quaker States, then it would be "Quaker States are in the lead."
I don't follow MLS, but looking at the team names, they mostly look singular to me, apart from "New York Red Bulls". I suspect the Red Bulls are nearly always referred to in the plural by Americans.
Joking aside, it might sound odd to an American (or Canadian?) but British English would not distinguish between whether or not the name or “nickname” are singular or plural. So we would say:
The Seahawks are winning
Seattle are winning
Arsenal are winning
Rangers were relegated
I think this is the kind of thing where you can learn to tolerate the “wrong” one but it’ll always sound weird to you, whether “wrong” for you is British or US English :-)
Edit: I did think of a situation where we’d use “is” - when you’re referring to the legal entity or FULL name of the club. “Aberdeen Football Club is a Scottish professional football club based in Aberdeen”. This is pretty rare to see, and you’ll likely just see it in, ironically enough, the first line of a Wikipedia page.