Cheating (also called gulling) is an act of lying, deception, fraud, trickery, imposture, or imposition. Cheating characteristically is employed to create an unfair advantage, usually in one's own interest, and often at the expense of others. Cheating implies the breaking of rules. The term "cheating" is less applicable to the breaking of laws, as illegal activities are referred to by specific legal terminology such as fraud or corruption. Cheating is a primordial economic act: getting more for less, often used when referring to marital infidelity.

Sport

see: Doping (sport) Another venue where cheating has occurred is in sport. An implicit agreement exists among participants that they will play by the rules and eschew unfair measures to win. Cheaters violate the spirit and/or the letter of the rules of competition. Examples include Ben Johnson's disqualification for doping in the 1988 Summer Olympics or the admissions of steroid use by former professional baseball players after they have retired, such as José Canseco and Ken Caminiti.

Cheating refers to more than using illegal substances. Perhaps the most famous example of cheating in professional sport took place in the 1986 FIFA World Cup when Diego Maradona used his hand to punch the ball into the back of the net past the England goalkeeper Peter Shilton. Using the hand or arm by anyone other than a goalkeeper is illegal according to the rules of association football.

Another example of cheating frequently seen in sports is the use of non-regulation (vis-a-vis the rules) equipment. In baseball, a pitcher using a doctored baseball (e.g. putting graphite or Vaseline on the baseball, or a batter using a corked bat are some examples of this.

Yet another example of cheating happened in the 1969 Sydney Rugby League Grand Final in which the South Sydney Rabbitohs played the Balmain Tigers. The Tigers over exploited a time delaying rule which stopped play. A Balmain player would fake an injury whenever Balmain were stretched and on the defensive. This would cause the referee to stop play and thus enable Balmain to reform their defensive line. As a result the game went on for 20 minutes more than its normal playing time.

Circumvention of rules governing conduct and procedures of a sport is also cheating. Erstwhile Indiana University men's basketball coach Kelvin Sampson was ousted from his position for persistent circumvention of rules. Sampson, over a period of 7 years (including his tenure at The University of Oklahoma) circumvented an NCAA rule designed to protect minor student-athletes from incessant interruption of their home lives and studies. The rule forbids college coaches from contacting student-athletes during periods when students are expected to be focusing on school, family life, and high-school team practices. Between his tenure at Oklahoma and Indiana, Sampson evaded this rule over 600 times, thus giving his teams an unfair recruiting advantage over opponents.