Canadian football vs rugby ball

Canadian football

noun
  • A game similar to American football played on a field of 110 yards long and 65 yards wide (with two 20 yard-long endzones) in which two teams of 12 players attempt to get an ovoid ball to the end of each other's territory. 

rugby ball

noun
  • A spheroidal ball designed for the sport of rugby. 

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