Very severe counter rotation. He’s got his back to home plate.
This can be corrected with wall drills. Search the forum for any of my posts mentioning how to conduct the wall drill. It fixes the problem without discussion. I love it. You don’t have to be worried about him not listening to you, if you don’t have to talk.
It will fix, without words, counter rotation, hands away from the body. It will also get his momentum moving toward home plate instead of backward because he will hit the wall if he tries to go backward. This will get him leading with the front hip.
Stand in the set position on flat ground with the outside of your pivot foot against the base of the wall. Now, with your arms folded across your chest, try to get up to your lift position. The goal of this drill is to teach your body how to get to the top of your lift without bouncing off the wall. In order to achieve this you will have to get your body moving both forward and upward together. After you get the feel for this movement, do about 30 reps a day until it’s something you no longer think about. Then you can progress to wearing a glove, striding forward and dry throwing from the wall.
I would also recommend the Hershiser Drill, just like someone else suggested.
Getting his momentum forward will also prevent injuries to his pivot knee. He’s almost got it turned 90 degrees internal to his hips during his lift–very bad for that joint.
He’s breaking his hands and he’s still got his back toward home plate. This is causing him to sweep his stride leg instead of striding forward to an equal and opposite position. He’s rotating his lower half into position which is very difficult to do with the precision necessary to get aligned down the target line. I fix this with a box. I put a cardboard box on the ground to the right of the target line. If he sweeps the leg, he kicks the box. Again, he gets reinforcement without a coach or parent having to say a word.
The early hand break and the slow lower half have him with his arm up prior to foot strike. This is a bad angle, but it also seems that his stride knee is right of his plant foot. This is an unstable base to transfer energy up the body. His shin should be vertical.
Since his upper half was ready before his lower half was, he has to slow down his upper half to let his lower half catch up. This is causing his hips and shoulders to be synced rather than separated. This problem should go away on its own if you can stop the counter rotation.
He has good external rotation.
Follow through is good.