verb (used with object), sandbagged, sandbagging.
3.
to furnish with sandbags.
4.
to hit or stun with a sandbag.
5.
Informal.
to set upon violently; attack from or as if from ambush.
to coerce or intimidate, as by threats:
The election committee was sandbagged into nominating the officers for a second term.
to thwart or cause to fail or be rejected, especially surreptitiously or without warning:
He sandbagged our proposal with his snide remarks to the boss.
6.
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.
Informal. to gain an advantage over (one or more competitors) by concealing one's abilities or other strengths early in a game or other competitive activity.
Informal. to gain an advantage by concealing or downplaying the strengths of (something):
companies that sandbag their earnings estimates and then easily beat them to make everyone happy.

Word Origin and History for sandbag Expand
n.
1580s, from sand (n.) + bag (n.).

v.
1860, "furnish with sandbags," from sandbag (n.). Meaning "pretend weakness," 1970s perhaps is extended from poker-playing sense of "refrain from raising at the first opportunity in hopes of raising more steeply later" (1940), which perhaps is from sandbagger in the sense of "bully or ruffian who uses a sandbag as a weapon to knock his intended victim unconscious" (1882). Hence "to fell or stun with a blow from a sandbag" (1887). Related: Sandbagged ; sandbagging.