Absolutely, horribly illegal.

Hey you know how it's legal to bet on wildfires? It would sure be nuts if people started legally betting on flock camera vandalism.

Since polymarket (& friends) is now somehow legal gambling (due to its political connections), one could bet against the event of flock cameras suddenly failing, and then somehow lose that bet due to unforeseen incidents...

I don't think you can make expanding foam balls in your garage that would work. You would need to encapsulate the pressurized polyurethane and seal it in something strong enough to withstand the gun launching it. Just loading marbles on the other hand...