My barrel horse cant lope in small circles without falling down everyone that sees this says its because hes stiff in his back legs how can i get him to loosen up?

Have you had your horse vet-checked? That's the first thing I would recommend. Your vet can perform a soundness exam and diagnose any soreness issues or joint problems that are causing the horse to stumble or fall.

the first thing I would do. I would go get him a vet check. then i have some stuff and its called DRAW!! Its the bust!! I use it on all my barrel horses and helps with pane and their joints. You can even use it on you.