I too was skeptical last year when I saw this changeset, from a brand new account... but I surveyed and there is indeed a skate apparatus there. It was drawn as a crude polygon, which I changed to a node pending updated aerial imagery.

I'm not a skater myself so I trusted the tags of the original mapper, Jane V Moses, who added "description=mini pumptrack" (which is actually still tagged on the flagpole) so I guess that's what it is. You can see it in the article about labyrinths that akadouri posted to #local-nyc -- https://gothamist.com/news/new-york-city-is-filled-with-labyrinths-if-you-know-where-to-look

Anyway I'm putting this back, and I'll add the flagpole as its own node.