ballpark vs playing field

ballpark

noun
  • A field, stadium or park where ball, especially baseball, is played. 

  • The general vicinity; somewhere close; a broad approximation. 

verb
  • To make a rough estimate of. 

adj
  • Approximate; close; on the right order of magnitude. 

playing field

noun
  • A field on which a game, especially a ball game, is played. 

  • Any place or context within which competitive activity takes place, such as market competition between companies. 

How often have the words ballpark and playing field occurred in a corpus of books? (source: Google Ngram Viewer )