backing vs leg up

backing

noun
  • Support, especially financial. 

  • A backdrop. 

  • The mounting of a horse or other animal. 

  • The action of putting something back; a switching into reverse. 

  • A liner or other material added behind or underneath. 

  • Musicians and vocalists who support the main performer. 

adj
  • Providing support for the main performer. 

leg up

noun
  • Assistance, help given to get started or overcome a problem or obstacle. 

  • A boost, a sudden improvement; an advantage, an edge. 

  • The act of assisting another's progress over a wall or other obstacle by forming a step for one of their feet with one's hands. 

How often have the words backing and leg up occurred in a corpus of books? (source: Google Ngram Viewer )