What Does It Mean?

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From our dictionary:
sand•bag

(sand'bag"), n., v., -bagged, -bag•ging.

—n.

1. a bag filled with sand, used in fortification, as ballast, etc.
2. such a bag used as a weapon.

—v.t.
1. to furnish with sandbags.
2. to hit or stun with a sandbag.
3. Informal.
a. to set upon violently; attack from or as if from ambush.
b. to coerce or intimidate, as by threats: The election committee was sandbagged into nominating the officers for a second term.
c. to thwart or cause to fail or be rejected, esp. surreptitiously or without warning: He sandbagged our proposal by snide remarks to the boss.
4. Poker. to deceive (one or more opponents) into remaining in the pot by refraining from betting on a strong hand, then raising the bet in a later round.

—v.i.
Poker. to sandbag one or more opponents.