Is there a word for representing one's self as weak or unintelligent in order to lull an opponent into a false sense of security and thus gain advantage? I have been using "disingenuous" but that's not correct.
The term I usually hear is
sandbag v, v tr
To downplay or misrepresent one's ability in a game or activity in order to deceive (someone), especially in gambling: sandbagged the pool player by playing poorly in the first game when stakes were low.
The etymology is interesting and instructive. From Etymonline:
. . . 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).
I take from this that the sandbag so mentioned must have been a non-obvious weapon that would have taken the victim by surprise.
In the context of gambling, you can use hustle:
To lure less skillful players into competing against oneself at (a gambling game)
For other contexts, there's the idiom play dumb:
To pretend to be slow-witted or lacking in specific knowledge, usually in order to avoid responsibility or to gain some advantage
TV Tropes also has a whole page on this phenomenon, which it calls Obfuscating Stupidity.
Dishonesty is a stratagem of tricksters, hustlers, and slimy, double-crossing, no-good swindlers; who would use ruses, ploys, subterfuge and/or illicit or fraudulent acts, in order to deceive you.
dishonesty, noun, dis·hon·es·ty, \–nə-stē\ -MW
lack of honesty : the quality of being untruthful or deceitful
1: lack of honesty or integrity : disposition to defraud or deceive
2: a dishonest act : fraud
swindler: a dishonest person (see scoundrel: Lando Calrissian)
stratagem, noun, strat·a·gem \ˈstra-tə-jəm, -ˌjem\ -MW
a trick or plan for deceiving an enemy or for achieving a goal
1.a : an artifice or trick in war for deceiving and outwitting the enemy
1.b : a cleverly contrived trick or scheme for gaining an end
2 : skill in ruses or trickery
ruse, noun \ˈrüs, ˈrüz\ -MW
a trick or act that is used to fool someone; a wily subterfuge
ploy, noun \ˈplȯi\ -MW
a clever trick or plan that is used to get someone to do something or to gain an advantage over someone
2.a : a tactic intended to embarrass or frustrate an opponent
2.b : a devised or contrived move : stratagem
subterfuge, noun, sub·ter·fuge \ˈsəb-tər-ˌfyüj\ -MW (See stratagem)
illicit, adjective, il·lic·it (ˌ)i(l)-ˈli-sət\
: not allowed by law : unlawful or illegal
: involving activities that are not considered morally acceptable
fraud, noun, \ˈfrȯd\ -MW
: the crime of using dishonest methods to take something valuable from another person
: a person who pretends to be what he or she is not in order to trick people
: a copy of something that is meant to look like the real thing in order to trick people