Teddy was real bad on a leash too. He's just a 3 lb pomeranian. When I'd put a leash on him, he'd flop around like a fish out of water. I was so afraid he was going to hang himself and/or die of fear that I didn't leash him for a few months. Just recently, I did what everyone is suggesting. I put a leash on him and just let it hang. I stayed near by so he didn't panick to much. He flopped around hysterically for about 1 minute. Then he stood still for probably an hour. By the end of the day, he was running all over the house dragging the leash. I had him leash trained within two days.

Your dog probably was beaten by a leash.