From Longman Dictionary of Contemporary Englishby the scruff of the neckby the scruff of the neckHOLDif you hold a person or animal by the scruff of their neck, you hold the skin, fur, or clothes at the back of their neck → scruff
Examples from the Corpus
by the scruff of the neck• It just caught me by the scruff of the neck and practically hammered my guts out.• One had hold of the other by the scruff of the neck and had fetched blood.• Three were dragged back on to the train and taken by the scruff of the neck from station to police car.• Your eyes narrow against the claws gripping you by the scruff of the neck until you let your hook of anger go. 