bullpen vs hole in the wall

bullpen

noun
  • The relief pitchers of a team collectively. 

  • A place for someone or something to get ready. 

  • An enclosed area for pitchers to warm up in during a game. 

  • An enclosed area used to hold bulls. 

  • An open seating arrangement where project teams can communicate openly with minimal effort. 

hole in the wall

How often have the words bullpen and hole in the wall occurred in a corpus of books? (source: Google Ngram Viewer )