American football vs black bag

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 bag

noun
  • The pouch or case traditionally carried by medical doctors, especially when making house calls, and containing medical instruments and supplies. 

  • A pouch or case containing burglary tools. 

  • A black plastic sack produced for the disposal of household waste. 

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