sandbag

a bag filled with sand; used as a weapon or to build walls or as ballast

treat harshly or unfairly

compel by coercion, threats, or crude means; "They sandbagged him to make dinner for everyone"

hit something or somebody as if with a sandbag

downplay one's ability (towards others) in a game in order to deceive, as in gambling

protect or strengthen with sandbags; stop up; "The residents sandbagged the beach front"