@rl.harris a horse brass usually has a bar at the top where it attaches to the leather. This has an odd "clip" at the bottom that either attaches to something or something attaches to it. The bar on the back looks like where it would attach or be sewn on.
It looks a bit like the finial of a pouch belt.
My guess is a belt plate style ornament, but the shape is ambiguous. Is it meant to be an exploding grenade or a crude Fleur-de-lis ?