rugby union vs soccer

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. 

soccer

noun
  • association football. 

verb
  • To kick the football directly off the ground, without using one's hands. 

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