Anybody who throws with just his arm is asking for big trouble. I don't have to see any video or the like to tell you that this kid, first and foremost, must learn "The Secret"---something I never tire of talking about because it really is one of the most essential elements of sound mechanics. He has to learn to get his entire body involved in the process, and a good place to start is with the "Hershiser" drill which aims at getting the hips fully involved. All he needs to do this is a fence or (preferably) a wall.
I learned "The Secret" many moons ago when I used to go to the original Yankee Stadium and saw what the members of the Big Three rotation were doing and how they were doing it. They were driving off the lower half of the body, using the legs, the hips and the torso in one continuous motion, to create a nonstop flow of energy all the way up through the shoulder and arm to the fingertips, thus generating more power behind their pitches---even Eddie Lopat who was not a fireballer---so they threw harder and faster with less effort and took a lot of pressure off said arm and shoulder in the process. I made a note of it and started working on it, and I quickly found that I was doing the same thing they were doing, with excellent results. It also didn't hurt that I was a natural, honest-to-gosh sidearmer with a consistent release point! (Not to mention the crossfire which I picked up in the process and which Lopat, who became my pitching coach, helped me refine.)
Once this kid masters "The Secret" a lot of other elements will fall into place, and he'll be on his way to becoming a better pitcher. pitcher. :baseballpitcher: