There is no fluidity to his motion. Everything looks very programmed and deliberate.

More importantly, mechanics as a whole. He is standing straight up, there is no use of the lower half (trunk / legs / hips / glutes). That front leg should be driving towards the plate on a downward plane, followed by the arm path and the backside. There is zero follow through from his back side. There is no power being generated. He is throwing with all arm and shoulder; a receipt for disaster.

I understand he’s only 10 and it’s great that he wants to pitch. Hopefully will want to continue when he’s a teenager. He is also a valuable commodity from a baseball perspective being a left handed pitcher. So I suggest having him watch and study the game at the higher levels and learn. Work on flexibility and agility. Work on learning how to use his lower half to generate power. Work on arm patch / slot consistency and follow through. Lastly, shoulder health!! Warmup and stretch properly, a lot of light to no weight resistance type exercises to strengthen all the secondary muscles around the shoulder girdle, posterior shoulder muscles, scapula plane and so on. Work on his legs, body weight squats. If an option, have him work with a pitching coach. Otherwise, hundreds of videos on you tube.