butt heads vs combat

butt heads

verb
  • To struggle against something that does not give way. 

  • To argue uncompromisingly. 

combat

verb
  • To fight; to struggle against. 

  • To fight (with); to struggle for victory (against). 

noun
  • A battle, a fight (often one in which weapons are used). 

  • a struggle for victory 

How often have the words butt heads and combat occurred in a corpus of books? (source: Google Ngram Viewer )