American football vs league

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. 

league

noun
  • An organization of sports teams which play against one another for a championship. 

  • A group or association of cooperating members. 

  • A stone erected near a public road to mark the distance of a league. 

  • The distance that a person can walk in one hour, commonly taken to be approximately three English miles (about five kilometers). 

  • A class or type of people or things that are evenly matched or on the same level. 

  • A prefecture-level administrative unit in Inner Mongolia (Chinese: 盟). 

  • An alliance or coalition. 

verb
  • To form an association; to unite in a league or confederacy; to combine for mutual support. 

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