Glove-side: Two distinct issues, I think, but they may be related. First, your son’s glove looks far too large for his size, and for his role as a pitcher. I’m guessing that glove weighs upwards of 2 lbs, and in the other hand he is holding (and trying to throw with a consistent release point) a 5 oz baseball. My 15 yo pitcher is 6’2", weighs 175, and his glove is smaller (and I’m guessing quite a bit lighter) than your boy’s glove. There is a lot to be said for maintaining good dynamic balance between the throwing arm and the glove-side arm during launch of a baseball.
The other glove-side issue, again, possibly related to the glove itself (but possibly an independent problem as well) is lack of glove-side arm stability before the ball is released.
During launch of the baseball, i.e., between the point of maximal external rotation (when the forearm lays back) and release of the ball, elite pitchers swivel their glove into place somewhere out in front of the torso…often approx. above the stride foot…and they stabilize it briefly out there while they bring their torso forward to meet the glove (not the reverse…i.e., “pulling the glove in”).
Your son looks to me like he is dropping that glove down to his side before ball release.
Tom House has discussed this common pitching flaw quite a lot in his recent books, and certainly at all of the pitching clinics he holds…glove control (based on the nmemonic phrase “swivel and stabilize”) is a very important issue for controlling the release point. It’s huge.
Eventually, your son might also want to start getting his front hip going toward the target before his leg lift is completed. Generating early momentum toward the target, besides helping with velocity, can also help somewhat with dynamic balance. Conversely, if he needs to create all of his forward momentum after the top of his leg lift, while trying to maintain static balance on one foot, that is just not as effective for most young pitchers. There are some guys who can do that very well, but they are the exception.
[Note added in edit: Start using a tripod when you videotape your son’s sports motion–the difference in ‘watchability’ will be stunning, I promise]