Really not all that terrible for a young kid and I’m giving my advise based on his age and teaching him the basics of pitching.
#1. First of all I think his glove is to big and heavy for him to control and therefore messing with his balance. If you watch, it ends up in various locations after he throws and then quickly drops to his side. I like to see it end up in the chest area to belt area and held there through-out the follow-through.
#2. Where he starts on the rubber is immaterial. What is important is your line.
Jacob sets up in a stance with the front foot more toward third, still OK. When he lifts and then lowers his leg he is establishing his path to be to the third base side of the plate. I think he needs to be more in line with the center of his body. I’d start by eliminating the offset front foot. He can go back later once direction and balance are solidly engrained. This will keep him in balance and moving in a straight line to his target.
#3. I’d like to see a quicker upward movement on the take away of the ball. More of a quick swing up, it’s a personal preference. Again, this keeps everything in the proper line.
#4. You have a line drawn on the ground for him to follow to the target. He often steps to the left. I think the initial location of the front foot contributes to the swing that takes to foot that direction and he’s just gotten used to it landing there. He goes up, (offset) down (offset), out (offset), then changes direction and ends up to his left.
#5. Finally, I see his follow-through needs polishing. He’s quick to standup, sometimes as he’s throwing and often before he finishes his follow-through. His right hand also doesn’t stay on line. Look at where he goes after he releases the ball. Sometimes it’s at the belt, sometimes at the thigh but seldom at or below the knee, where I think it should be. I also think he’s head and eyes need to follow the ball to the target. I used to tell my kids, put your chin in the glove to give mental image of following the pitch to the target.
My summary: not real bad and a lot of his issues start with balance and direction. Fix those and then address the next action, there will always be something else.
I’m not a professional by any means, just a dad a few years ahead of where you are. I’m giving you several thousands of dollars of advice giving to my son through the years.