I remember reading about a kid like this at a California school. He was kind of fat, very out of shape, but he could throw a ball pretty hard, low 90's. Early in spring training the team's crazy strength coach started riding the kid, calling him fat, lazy, etc. He challenged the young man to really get in shape for the first time in his life. It hurt the guy's feelings, but he decided to give it a try. After a while, this kid found that he was starting to enjoy the feeling of being in better shape, so he really took to weight training. He lost several bags of weight, got a lot stronger, and his fastball velocity shot up to the upper 90's, even 100 mph. Eventually, Stephen Strasburg got drafted, made it to the show, and has been doing pretty well since then.