Good morning!
It was a busy day at work ...
Short answer: no idea.
My first guess was "a small wrecking ball", but it's too small, too light, and isn't all banged up. Besides, there no Miley Cyrus with it.
Then, like Ken, "maybe some kind of exercise thingy" ... for people with very small hands. The "kettlebell" would have been right on, but at most we could stick our fingers into those holes.
I also liked the idea that "a rope could thread through those holes". But it wouldn't float, so it isn't to hold a net up. Maybe weights for the bottom of a net, to hold it down?
Sorry!