@OnDeedolito—
Even if one takes this as a alternative history in which what they are doing evolved from Mediaeval tournaments, the result of that evolution was still LARPing, and they are still LARPers. That's why the
mangaka draws upon LARPing in the explanatory
omake.
Now, I have not criticized LARPing as such; but the portrayal of it as
magnificent — no matter what the imagined history — is doomed to commercial failure.
Popular fiction about
gladitorial combat — not about LARPing, but about contestants seeking each to injure the other — has a significant commercial footprint.
To make
prancing football (a.k.a. “soccer”) akin to LARPing, one would replace the ball with a very obviously fake human head, and then engage in some great pretense of how significant the head as such were. As it is, yes, prancing football has wide social appeal despite its silliness, but the appeal is on a different basis.