"Scruff of the neck" is a colloquial term that refers to grabbing someone or something by the loose skin at the back of the neck. It is often used in a metaphorical sense to describe situations where someone is taking control of a difficult person or situation. If you're looking for synonyms for this term, there are a few options. One is "nape of the neck," which is the anatomical name for the same area of loose skin. Another is "collar," which can be used both literally and metaphorically to describe grabbing hold of someone or something with authority. Lastly, you could use "neck grip," which is more descriptive but less common than the other options.