Hi, it definitely sounds like he has sprained or hurt his leg, probably from playing too rough or from jumping down from the wall. He could have landed wrong. I would take him to the vet, where he can feel his leg, and take an X-ray if necessary to make sure he didn't break something, the paws and the ankle bones have so many little bones. Even if he sprained it, he could be in pain, bullies have a high pain threshold and often don't show it, but being lethargic, limping, or favoring his leg, and yelping when you touch it are all signs that he is experiencing pain. The vet will be able to determine the injury, and also prescribe him a pain medication and an anti inflammatory if he has sprained it. When I first brought my male Bulldozer home, I had him out in my front yard, and all the neighbours came running over to see the new puppies, after they left, I picked Dozer up to take him back in the house, I had him in my arms, and I bent down to get Blossom, Dozer got all excited to see his sister, and he squirmed and jumped out of my arms onto the grass. Thank goodness I was bent over the grass, so he didn't fall too far, but He landed wrong on his front paw, and he yelped so loud, that my neighbour down the complex came running. We were both crying, I felt so bad for him falling. After he stopped yelping, he wouldn't walk on that front leg, and he kept it up in the air and favoured it. If I touched it, he yelped, the sound was so awful, he cried so loud, it broke my heart. I called the emergency vet, because it was in the evening and Sunday, so my vet was closed. They told me we could wait until the morning and take him to our own vet. I put him on my cat bed because it was soft and had him sleep beside me on my bed. When he had to go out to potty, I carried him outside, and every time I moved him, he would cry. I went to the vet first thing in the morning, my vet took him in right away and she checked his leg and paw, she said she didn't think he had broken anything, and that she couldn't feel anything out of place, but wanted to X-ray his leg, she did an X-ray of both the front legs, so she could compare the two. Nothing was broken or out of place, so she said he had sprained his foot. It wasn't the leg, but the paw part. She gave him a shot of inflammatory medication, and some pain pills. She told me to keep him quiet, and not let him jump. He favoured that paw for 4 days, before he started walking on it again, and then he was fine. I would let your vet look at his leg, just to rule out if its broken or not, and to get him some pain medications so he can be comfortable. I hope he feels better soon, and that it's nothing serious.