It sounds like what he's doing is trying to shift the contents of the crop around to get it to empty. Likely there's something in the way.
At the bottom is a link to a really good guide on what to do for just about everything concerning the crop. Until the crop reduces, no food, no water. You could attempt to empty the crop out through the mouth, ("vomiting") -- but that does indeed carry the risk that he'll get some of it down his windpipe or basically choke if what comes up blocks the airway. I've done it with success, but it's very important to recognize the risk involved.
Sometimes a non-moving crop can be the first really noticeable symptom of another disease process and signals the end could be near, however it could also be as simple as he ate a leaf or a bunch of feathers or tall grass or straw ... that are blocking the crop.
https://www.backyardchickens.com/ar...d-sour-crops-prevention-and-treatments.67194/