by the scruff of (one's)/its/the neck
By the back of the neck (of a person or animal). My mom was so mad that she grabbed me by the scruff of the neck and hauled me into my room to be grounded. I had to yank the cat out from under the floorboards by the scruff of its neck. The boss took John by the scruff of his neck and warned him never to do something so foolish again.
by the scruff of somebody’s/the ˈneck
(hold somebody or an animal) by the back of the neck: The barman took her by the scruff of the neck and threw her out.