backflip vs forward roll

backflip

noun
  • An act of rotating one's body 360 degrees in the backward direction. 

  • a total reversal in policy or opinion; a volte-face, a U-turn. 

verb
  • To perform a backflip (rotation of body). 

  • To completely reverse a policy or opinion; perform a U-turn. 

forward roll

noun
  • A movement in which one's body is rolled forward, by putting the head on the ground and swinging the legs over the head. 

How often have the words backflip and forward roll occurred in a corpus of books? (source: Google Ngram Viewer )