The phrase "underdog story" refers to a situation where someone who is not expected to succeed or win something ends up overcoming the odds and achieving victory. Full definition
He doesn't know he's supposed to fail, and as a result has achieved more than anybody thought was possible — a true underdog story in every aspect. (stubbydog.org)
Without exaggeration, it could be the greatest underdog story in the history of sports. (sportsinsights.com)
While everyone loves a good underdog story, our reason for betting against the public has nothing to do with cheering for the little guy... and everything to do with value. (sportsinsights.com)