back up vs foul

back up

verb
  • For a fielder to position himself behind the wicket (relative to a team-mate who is throwing the ball at the wicket) so as to stop the ball, and prevent overthrows. 

  • For the non-striker to take a few steps down the pitch, in preparation to taking a run, just as the bowler bowls the ball. 

  • To move backwards, especially for a vehicle to do so. 

  • To copy (data) so that it can be restored if the main copy is lost. 

  • To undo one's actions. 

  • To fill up because of a backlog. 

  • To halt the flow or movement of something. 

  • To provide support or the promise of support to. 

  • To reconsider one's thoughts. 

  • To move a vehicle backwards. 

  • Coordinate terms: back away, back off, stand back 

foul

verb
  • To hit a ball outside of the baselines. 

  • To make contact with an opposing player in order to gain advantage. 

  • To become clogged. 

  • To become entangled. 

  • To come into contact or collide with. 

  • To make dirty. 

  • To besmirch. 

  • To hit outside of the baselines. 

  • To clog or obstruct. 

  • To entangle. 

  • To commit a foul. 

noun
  • A breach of the rules of a game, especially one involving inappropriate contact with an opposing player in order to gain an advantage; for example, tripping someone up in soccer, or contact of any kind in basketball. 

  • A foul ball, a ball which has been hit outside of the base lines. 

  • A (usually accidental) contact between a bowler and the lane before the bowler has released the ball. 

adj
  • Entangled and therefore restricting free movement, not clear. 

  • Detestable, unpleasant, loathsome. 

  • Obscene, vulgar or abusive. 

  • Disgusting, repulsive; causing disgust. 

  • (with "of") Positioned on, in, or near enough to (a specified area) so as to obstruct it. 

  • Dishonest or not conforming to the established rules and customs of a game, conflict, test, etc. 

  • Unpleasant, stormy or rainy. 

  • Covered with, or containing unclean matter; dirty. 

  • Outside of the base lines; in foul territory. 

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