American football vs black box

American football

noun
  • A game similar to rugby football played on a field of 100 yards long and 53 1/3 yards wide (with two 10 yard-long endzones) in which two teams of 11 players attempt to get an ovoid ball into each other's territory. 

black box

verb
  • To focus on the inputs and outputs without worrying about the internal complexity. 

noun
  • A flight recorder; the brightly colored cockpit voice recorders and flight data recorders in an aircraft designed to aid in determining the cause of an accident. 

  • A device used in phreaking that prevents the calling party from being billed for the call placed. 

  • A type of theater characterized by a lack of decoration or complex mechanisms. 

  • A theoretical construct or device with known input and output characteristics but unknown method of operation. 

  • Any similar device on motor vehicles, such as rail event recorders and ship trip recorders. 

How often have the words American football and black box occurred in a corpus of books? (source: Google Ngram Viewer )