I'm not sure, I'd never 'Saints is winning'. 'Saints are winning' sounds correct, though. Even 'Arsenal is winning' sounds a bit wrong.
Whos winning? Arsenal are (team)
Whos winning? Ronnie O'Sullivan is (singular)
Disclosure: I am English.
Whos winning? Arsenal are (team)
Whos winning? Ronnie O'Sullivan is (singular)
Disclosure: I am English.
Arsenal are winning
Arsenal is the best team in the league
It's contradictory (as well as plainly false ;) ), but that's English.
https://twitter.com/search?q=%22arsenal%20are%20the%20best%2...
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.