Green’s Dictionary of Slang

1. to feign weakness in order to mislead; to evade one’s responsibilities.

1932		(con. WWI) L. Mann Flesh in Armour 291: The man had spent a year in the clink for sand-bagging when overstaying leave.
1961		(con. early 1950s) J. Peacock Valhalla 139: You sandbagging bastard. I can see you’re busy as hell.

2. (poker) to resist raising the bet immediately in the hope of making a larger raise later on.

1938		E. Culbertson Games Digest 2 9: In some circles it is the custom to ‘sandbag’ by failing to knock when able, the player hoping to beat some other knocker.
1944		Liquorian 32 11: Players pass, bid, finesse, lead, renege, echo, and sandbag; they rob the deck, they play rubbers.
1955		Amer. Eagle 12-14 n.p.: Knowing a poker game was in the offlng. some of our teamsters [...] showed us the fine points of checking a cinch, how to sandbag, the correct way of shorting the ante and how to lay in the weeds.
1968		Life 16 Aug. 42: The bookie was cagey enough to ‘sandbag’ (not bet and encourage weaker hands to do so and build the pot).
1972		Playboy’s Bk Games 22: A third party staying in will have much better chances to draw and sandbag both of you.
1999		E. Bunker Mr Blue 63: Fuckin’ kid sandbagged me.