Hurt jack russell

Question
A friends two dog were running in the yard playing and all of a sudden the jack russell yelped and stopped running. Now she is walking with her back leg lifted up or limping, but I have seen her use it to jump on the couch and to stand on her back legs. Could it be a sprained muscle or tendon? The dog has no sensitivity to touch or movement anywhere on the leg, hip, or paw. ps I looked where she stopped running and I found a rock about the size of a golf ball in the grass. There is no sign or any kind of puncture or wound on the paw.

Answer
It's possible she bruised herself, or yes, sprained a tendon or muscle. If you can move her leg in total rotation and it doesn't hurt her, I would just keep an eye on it. A baby asprin will take away the pain, and keep her on restricted movement for the next two days. If she is still limping on the third day, a trip to the vet may be in order. Otherwise, she should be just fine.