/ ˈʌndədɒg; NAmE ˈʌndərdɔːg/ noun
a person, team, country, etc. that is thought to be in a weaker position than others and therefore not likely to be successful, win a competition, etc. :
Before the game we were definitely the underdogs.
In politics, he was a champion of the underdog (= always fought for the rights of weaker people) .