rugby football vs rugby shirt

rugby football

noun
  • A rugby ball. 

  • The sport of rugby: either rugby league or rugby union. 

rugby shirt

noun
  • A shirt of the kind worn by rugby players, usually short-sleeved and with a buttoned opening at the neck like a polo shirt, but with a stiffer collar. 

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