Thanks for the Note + photo. :)

Adjusted it in:

- https://www.openstreetmap.org/changeset/152649686

- - -

If the tent is "permanent", it would be marked as a:

- building=tent
- https://wiki.openstreetmap.org/wiki/Tag:building%3Dtent

The Wiki also says:

"In OSM only stationary **or at least seasonal tents** are to be mapped as buildings."

It looks like that concrete area inside the stadium is a section to temporarily put various "buildings" up—like on some satellite footage I see it's a big concert stage.

So I'd definitely say "tent". :)