"Plucky underdog" refers to a person or a team who is considered the lesser or weaker side, but displays great determination, courage, and resilience to achieve success or overcome challenges. Full definition
Take one plucky underdog of a hero, add in a disapproving relative / friend / acquaintance who pooh - poohs his dreams, throw in a preliminary test of his mettle that proves our hero's limitations, sprinkle a dash of «deus ex machina» to give him the edge he needs to succeed, hook him up with a weird and diverse support crew, toss in a villain drawn with broadly evil strokes, and bring it all to a boiling climax that begets the predictable happy ending. (theretroset.com)
Leicester are no longer viewed as plucky underdogs but as a club in position to make history. (eplindex.com)
From McLaren's clean and corporate image, to Renault's cheeky personality and Force India's plucky underdog character, Formula 1 teams are all very different. (wtf1.com)