introduce vs start the ball rolling

introduce

verb
  • To bring (something) into practice. 

  • To cause (someone) to be acquainted (with someone else). 

  • To add (something) to a system, a mixture, or a container. 

  • To make (something or someone) known by formal announcement or recommendation. 

start the ball rolling

verb
  • Synonym of get the ball rolling. 

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