To take hold of a person or animal's back of the neck in a sudden and rough way.
Figuratively: to take control over someone or something

I was just a kid and I remember that when I tried to go see that X-rated movie, the usher grabbed me by the nape of the neck and threw me out

Ero un ragazzino e ricordo che quando ho tentato di entrare a vedere quel film vietato ai minori, la maschera mi ha preso per la collottola e mi ha sbattuto fuori

I was at a rock concert and I was trying to go through the cheering crowd to get right under the stage, but someone grabbed me by the collar and threw me back

Ero a un concerto rock e cercavo di farmi varco nel pubblico stipato per raggiungere il palcoscenico, ma qualcuno mi ha preso per la collottola e mi ha respinto indietro