13yo 5'9" 130pds RHPwe are looking to increase velocity. Watching the video of my son I think that he could stride out a little more and he cocks his arm early. do you all agree and do you see anything else. apologize for the poor video.
Try to get some closer video., if possible... it's tough to see from this distance, but I'd like to see him brace up against a firmer front leg. Let us know if you've got some other video.
Definitely needs to get his center of mass moving forward sooner and faster. And needs to lead the early part of his stride with his front hip instead of reaching out with his front foot. Google "Hershiser drill".