Violins are a bit of a strange design. Classically you hold them up by pinching them between your chin and shoulder (restricting head motion), though in more casual contexts people sometimes use their left arm (restricting hand motion). Neither of these are great! Why can't the violin stay up on its own?

It can! People have made all sorts of straps, ribs, and counterweights for violins. Some examples:

Wickelbuckle:

NS Design Balanced Shoulder Rest:

Aceto Violin Neck Strap:

Violin Valet:

VioStrap:

I wanted something similar for my Stroh violin, and played around a bit. After trying a few things I ended up with a truly silly counterweight design:

Probably one of the other designs would have worked better, but this does have the advantage of a long lever. Those are literal rocks taped to the end.

I still probably won't play my Stroh very much, but I'm now much less likely to hurt myself when I do.