instigate vs start the ball rolling

instigate

verb
  • to goad or urge (a person) forward, especially to wicked actions; to provoke 

  • to incite; to bring about by urging or encouraging 

start the ball rolling

verb
  • Synonym of get the ball rolling. 

How often have the words instigate and start the ball rolling occurred in a corpus of books? (source: Google Ngram Viewer )