I had a yorkie about 20 years ago, weighed 5 pounds soaking wet. You could not wear this dog down. He loved to fetch and I threw a tennis ball over 100 times not stop, he never quit. I also use to hang the ball from the ceiling, about three feet off the ground. Teh little boogerwould jump straight up grab it and hang until I had to pry his mouth open. I guess this is the terrier in them, same as a pitbull.