knock back vs protest at

knock back

verb
  • To drink an alcoholic beverage swiftly or often. 

  • To stun; to surprise. 

  • To press or knead (dough) so as to remove air bubbles. 

  • To reject; to refuse. 

protest at

How often have the words knock back and protest at occurred in a corpus of books? (source: Google Ngram Viewer )