Bottom line a improper swing plane.
Ok for a simple dad like me lets keep this ultra simple on things to work on to fix...this is what "I think" I got
1.shoulders need to rotate more on the swing
2.rear elbow should be kept away from the body.
The rest I'm uncertain what you all are suggesting.
The rear and front shoulder should do what?
Is there anything that breaks a swing down frame by frame what a player should be working to do at each point?
Yeah the rear elbow does pin to the torso. Good call.
How many frames are you seeing this pinning of the rear elbow to the torso? Can you make a GIF showing this pinning?
The back elbow stays at the side while the hands turn the barrel into contact. It doesn't flow through the contact position. I'll make a gif.