So many things can cause this and it is hard to diagnose without an x-ray and the attention of a vet that specializes in herps. I could be from shock or a spinal injury. It also could be caused by such things are infection and parasites.
If your willing to take on the financial part of attempting to save the frog then see a vet, if not then you can try to save him but without knowing the cause there is no way to suggest a path to try and help the frog besides a safe place to rest. If going that route, put wet paper towel on the bottom of the container (wet with dechlorinated or spring water) and mist it a few time each day.
Your also going to have to try feeding if your going to try and save him.