front line vs front man

front line

noun
  • attack, collectively the attackers or forwards. 

  • A low level. 

  • A site of a conflict, effort, or controversial matter of any kind. 

  • A front, or a boundary between opposing positions. 

  • The site of interaction with outsiders, such as customers. 

front man

noun
  • striker, attacker, forward. 

  • A person acting as the public face of some other, covert group. 

  • The lead singer in a musical group. 

How often have the words front line and front man occurred in a corpus of books? (source: Google Ngram Viewer )