Underdog is what UDOG stands for. "Play like a Champion, train like an Underdog" is one of our mantra, one of the most powerful motivation quotes. When a champion plays, he/she plays like they are in control of all aspects of the game. They play to win. They know when and what to do. When an underdog practices he/she practices it with their full soul and body. They practice very hard as they know nothing, and they have nothing to lose or be egoistic of and leave the practice.
Authorship of the saying is unknown, it is sometimes credited to basketball star Michael Jordan.