hoover, that is what I was thinking. When I was at the vet with my mare, a lady who used to work there (whom id chat with about horses, of course) had her stud in there with an almost perfect wound in his shoulder, right at the point. His shoulder bone was also chipped. He lives in a pipe corral, so she thinks her neighbor shot him trying to get her dog, and wont fess up because he doesn't want the vet bill. I would post a couple cams out where you can see something if you can't find anything around the fences.
Also, when I was at my first barn in CA, my friend and I turned 4 arabians together out every day in a half wood, half pipe arena, and one of the arabian mares that wasn't broke yet, somehow ended up with a short screw in her head right in the hollow above the eye. It had to be removed via surgery.