on the line vs spearhead

on the line

prep
  • At risk, as in a contest or enterprise. 

  • Currently calling on the telephone. 

  • On one of the lines marked on a playing field or court; (by extension) within bounds. 

  • On a level with the eye of the observer, as of a picture hung in on a wall. 

spearhead

verb
  • To drive or campaign ardently for, as an effort, project, etc. 

noun
  • The leading military unit in an attack. 

  • One who leads or initiates an activity (such as an attack or a campaign). 

  • The pointed head, or end, of a spear. 

  • A player who initiates attacking moves. 

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