competitor vs opposite side

competitor

noun
  • A person or organization against whom one is competing. 

  • A participant in a competition, especially in athletics. 

opposite side

noun
  • A side, party (e.g. a team or armed force) seen as adversary, enemy etc. opposite one (or more) other(s), as in a battle or team sports competition. 

How often have the words competitor and opposite side occurred in a corpus of books? (source: Google Ngram Viewer )