It's something that there's a distinct advantage to working on and stopping.

Not because it's essential to bring him in to eat and to be calm.... because to be frank.... it isn't.

You could just do what others are suggesting and avoid the issue and feed him outside. But I personally don't recommend that at all.

Indeed I'd assert IF you can help him to be calm then IF he ever does REALLY need to be in a stable, say if he's unwell or injured, then he's not going to be totally stressed out and I'd say that's pretty important to do BEFORE you need it.

Horses box walk generally because they're bored, don't have social contact and have diets with incorrect forage and grain proportions.

I don't know what you've already tried or if when the horse is brought in what the environment is like for it in terms of the horse's near by it etc but there's things you can and ought to do in terms of such as ensuring the neighbouring horses are always the same ones and that they're calm. When he's out ensure he's in a herd.Lower internal stable walls so it's a half panel where he can interact with the neighbour. Design of stable with an external window and a door where there's plenty for him to see. Using a mirror. Stabling and doing this all when it's not the chaos and excitement of feed time. Providing interesting things for him to concentrate on: e.g. spreading his hay on the floor with bit of chopped carrots or apples in to search for and find. Putting lots of different textured things and things of interest in the food bowl. Using such as a food ball so he has to work for his food. Ensuring he's not getting too much feed stuff that's high energy that makes him act like a kid on junk food and that he's getting good and sufficient exercise to relieve boredom. Ensure there's plenty of forage.