association football vs rugby union

association football

noun
  • A ball game played between two teams of eleven players, each attempting to win by scoring more goals than their opponent. 

rugby union

noun
  • A form of rugby football, historically amateur, having 15 players per side; points are scored for a try, penalty, drop kick or conversion. 

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