As defined by Funk & Wagnalls:
underdog n. 1. One who is at a disadvantage in a struggle. 2. One who is victimized or downtrodden by society.
An underdog is anyone who has to face a higher level of
adversity to reach a goal (often
survival, or "winning") than either their opponent(s), contemporaries, or peers. Often the classic underdog is a
victim of an antagonizing opponent. Moreover, a
classic underdog
typically has positive qualities that are
absent in his or her stronger or
better armed opponent.