head start vs restriction

head start

noun
  • A factor conducive to superiority and success. 

  • An advantage consisting in starting a competition or task earlier than might be expected; given (or taken), for example, prior to the beginning of a race. 

restriction

noun
  • A regulation or limitation that restricts. 

  • The act of restricting, or the state of being restricted. 

  • The mechanism by which a cell degrades foreign DNA material. 

How often have the words head start and restriction occurred in a corpus of books? (source: Google Ngram Viewer )