American football vs rugby

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. 

rugby

noun
  • A form of football in which players can hold or kick an ovoid ball; rugby football. The ball cannot be handled forwards and points are scored by touching the ball to the ground in the area past the opponent's territory or by kicking the ball between goalposts and over a crossbar. 

  • The form of the game known as rugby union (see the usage note). 

  • Rubber cement, contact cement. 

verb
  • To play rugby. 

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