footy vs rugby ball

footy

noun
  • The ball used in a game of footy. 

  • A football fan. 

  • Football (association football) (soccer in US, Canada, Australia, New Zealand) 

  • The game or sport of football, usually Australian rules football or rugby league, but not soccer 

  • A short sock. 

rugby ball

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

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