I'd say that it is part of a recent ornamental/fantasy flail weapon. The turned spikes had to be secured inside the ball so to allow internal access a 2 piece construction, with a smaller bottom cap attached to the chain, would make sense. Being lightweight means it wouldn't likely seriously injure people. That was probably a good thing, as it seems someone was fooling around out on the water playing pirate or something when they broke their flail.
Ha! It is funny in just a few responses people here have the best guesses pegged that took a week to get to. The ball part is a little larger diameter than a baseball. The ball is made out of thick but not too heavy brass and the pegs are brass or bronze.
The peg at the top has a brass threaded stem holding it in and the next row seems to be riveted in and the lowest row is riveted and reinforced. Seems like a lot of effort went into it. I don’t see how a cap that would attach to a chain would attach to this piece... Doesn’t mean it didn’t it just doesn’t seem to have any marks from something attaching or hardware intended to make the connection.
It is a household debris field in an inland lake. Found everything from pontiled fruit jars in the past to my first mini jug this weekend and a crazy cool cast iron paddle wheel steamer toy. Everything seems to be pre date maybe 1920 with most being earlier.
The best guess from work aside from Mace/flail and lightening rod ball was warrior kitten helmet. Interestingly I did find a lightening rod finial with a brass spike on it out there too. That was last year. It had about forty feet of twisted soft steel rod attached to it. For sure this and that are unrelated. There is no way i can see that they could go together.