im thinking something injury related. Not sure if it is lacing, I don't know much about lacing, but has the horse ever been rode? Or are you adopting it unhandled?
The reason I ask is maybe its from an ill fitting breeching? Not sure what you call it, but its the piece that attaches to the back of the saddle, and goes under the tail, for a horse with mutton withers? That's a bit of a stretch, but maybe a possibility. I am still with an injury.
Baby, Sparta, Carmen, Henry, Hooch, Mercedes, Butterscotch