quad rugby vs wheelchair rugby

quad rugby

noun
  • Synonym of wheelchair rugby (US regional name and American English vernacular name) 

wheelchair rugby

noun
  • A variation of rugby played by players in wheelchairs, primarily players with some disability. It is a full-contact sport and is played on a hardwood court with a ball similar to a basketball. 

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