Need some advice for Glove side Head issues

My son has a tendency to look down at the ground as he is finishing his pitches. Which is affecting his accuracy. This seems to be caused by a weak glove side. I have tried verbal cues, like see the ball all the way into the glove etc. I have even tried having him hold a pair of clamps on his glove side to create some resistance. Has anyone had success with any drills or cues that may help with this head movement?

Ironically he does the same when he plays infield/outfield and actually is very accurate from these positions. But overall I just want to get his head from dropping

First thing to look at is what he does prior to the head movement and, in particular, his set-up on the mound. Make sure he’s not doing something earlier in the delivery that leads to the head movement.

Also, look at his tempo. The difference between pitching and playing in the field is that fielders usually need to get rid of the ball as quickly as possible so they move quickly through their delivery while pitchers can move a slowly as they want. You might want to have your son get himself moving down the hill sooner/faster.