i am definitely not an expert and it does look a little odd and possibly fabricated for personal use. I am not sure what kind of metal it is made out of; but, it sure looks like the individual who might have made it had a purpose. To me it looks like it might have been installed it in a manner that a force was exerted on the ball and translated through the arch. My only reasoning for this thought is the way the arch is constructed. Of course this is just a guess and for all I know a rope/wire or anything could have been looped through there.
From that point I thought a leather working tool, something for loosening knots/straps or something, or possibly a part off of some piece of equipment, or course it would be a tool then..
I appreciate the thoughts!