assist vs fall upon

assist

verb
  • To help compensate for what is missing with the help of a medical technique or therapy. 

  • To help. 

  • To make a pass that leads directly towards scoring. 

noun
  • A decisive pass made to the goal scorer 

  • A helpful action or an act of giving. 

  • A defensive play, allowing a teammate to record a putout. 

fall upon

verb
  • to experience; to suffer. 

  • to occur at some particular point in time. 

  • to set upon; to attack suddenly 

How often have the words assist and fall upon occurred in a corpus of books? (source: Google Ngram Viewer )