1.To treat harshly or unfairly.
2.To hit something or somebody with or as if with a sandbag.
3.To protect or strengthen with sandbags; stop up; as, the residents sandbagged the beach front.
4.To thwart (another person's plans) by surreptitious maneuvers; as, he sandbagged my proposal by talking in private with other members of the committee. (informal)
5.To intimidate or coerce, especially by crude methods. (Informal)
6.To deceive and take advantage of (a person) by misrepresenting one's true intentions. (Informal)
7.Hence: (Poker) To encourage opponents into betting more by first refraining from betting while having a strong hand, and only later raising the stakes. In informal games, certain types of sandbagging are forbidden.
