fall back in WordNet English dictionary

1. hang (back) or fall (behind) in movement, progress, development, etc.
   lag  dawdle  fall back  fall behind 
   
2. retreat
   fall back  lose  drop off  fall behind  recede 
   
3. go back to bad behavior
   "Those who recidivate are often minor criminals"
   relapse  lapse  recidivate  regress  retrogress  fall back 
   
4. fall backwards and down
   fall back 
   
5. move back and away from
   "The enemy fell back"
   fall back 
   
6. have recourse to
   "The government resorted to rationing meat"
   fall back  resort  recur 
   

fall back in English Wiktionary