beat off vs fight back

beat off

verb
  • To drive something away with blows or military force. 

  • To waste time. 

  • To masturbate, usually a man of himself. 

fight back

verb
  • to counterattack; to resist an attack. 

  • to defend oneself by fighting. 

  • to repress; to struggle to repress. 

  • to overturn a losing deficit. 

How often have the words beat off and fight back occurred in a corpus of books? (source: Google Ngram Viewer )