21.flashscore.ninja presents itself with a name that closely mimics the popular sports scores platform Flashscore, but the site itself is non-functional. When you visit, you get a 404 error page. That's a huge red flag. A legitimate website, even a small one, should at least load its homepage.
There is no information about who runs this site, no contact details, and no privacy policy. The domain name is the only thing that gives a clue about its purpose, and that alone is suspicious because it seems designed to confuse visitors expecting the real Flashscore. The site also has no history in the Wayback Machine, meaning it's either very new or was set up and quickly abandoned.
If you're wondering 'is 21.flashscore.ninja a scam', the safe answer is to treat it as one. There's no evidence of fraud, but there's also no evidence of a functioning service. The best advice is to avoid this domain entirely and stick with the official Flashscore website for sports updates.