Examine it closely when you crawl in there to cut it off.

tj

Contact your local extension. Plenty of bugs are microscopic and diseases are hard to see. They'll probably tell you where you can send a sample.

If it is only a single branch that is affected, it is very unlikely to be caused by an insect or disease. Other branches would also show signs of infestation. That sort of singular, isolated dieback is most often the result of mechanical/physical damage, even if not readily visible

looks about the size of a basketball or soccer ball.. any kids around???

prune it out.. leave no stub.. take some closer pix.. front and back...

agree that is it were bugs or disease.. it wouldnt be so localized ...

also.. if its really a GG they are rather bug proof..

where are you.. big city name...

most time leaf tissue turns brown. it doesnt recover on its own ..

that said.. a damaged branch is not the end of the world... prune it out...

no bug chems..unless you find an actual pest to get rid of..

ken

You have yellowing on the tips of other branches on that tree. There is a bug that damages arborvitaes. It's called something like Pestalotpistis. I've put a link about it below. Of course, few people can accurately ID a plant disease from a picture. But this is why I recommend your local extension. My local extension will diagnose plant disease for free. If yours doesn't, it's probably quite cheap.

What is it? What to do about it? | Ornamental Disease Facts (osu.edu)