Back in the Day
The word ''sandbag'' dates back as far as the 1580s, according to the Online Etymology Dictionary, and referred merely to a bag filled with sand, often used as a weapon. The noun evolved into a verb around 1887 meaning to attack someone with a sandbag, making a sandbagger a rotten individual who ambushed his victims with that sandbag. In the 1940s, sandbagging meant to hold back from betting at first in hopes of making a greater bet later. The modern meaning of the term took shape around 1970.