Match-fixing is a match in which the result, or important events within it, are determined not by the play itself but by a prior agreement. At least one participant deliberately does not play to win: they lose on purpose, give away a round or a map, or carry out pre-arranged actions. The concept comes from traditional sports, where it is also called match-fixing, and it is used in esports in the same sense.
What it looks like in practice
There are several variants. The simplest is "throwing": a player or an entire team deliberately loses a match while someone bets on their defeat with a bookmaker. Another variant is an agreement between two teams: for example, both are already advancing regardless of the outcome and decide in advance who will win, in order to help one of them with the bracket or the rankings. There is also a "soft" form, in which the match result is left alone but particular events are agreed in advance: who will take the first map, how many rounds there will be, who will get the first kill. Bets can be placed on such events too, and they are just as dangerous.
A typical situation: a strong team suddenly plays noticeably worse than usual, makes inexplicable mistakes and fails to use obvious opportunities, while an unusually large volume of bets on its defeat appears shortly before the match. Suspicion often begins with exactly this combination.
Why people do it
The main motive is money. Betting on esports turns the outcome of a match into a commodity, and anyone who knows the result in advance can profit from it. Less often, the reasons are different: a wish to avoid a strong opponent in the bracket, a favorable setup in the tournament table, or pressure from third parties.
How it is detected
Tournament organizers and companies that monitor competitive integrity analyze betting anomalies, study recordings of games (demos, that is, match replay files) and players' actions, and cross-reference correspondence and other evidence. Strange in-game mistakes alone are usually not enough for punishment: confirmation of intent is needed.
What it leads to
The rules of most tournaments prohibit not only taking part in fixed matches but also betting on one's own games, as well as concealing information about offers to fix a match. Penalties vary: annulment of results, disqualification, lifetime bans for players and coaches, and forfeiture of prize money. For teams it is also a reputational blow, after which sponsors and organizers often refuse to work with them.
Match-fixing is widely regarded as one of the main threats to esports: if viewers stop believing in the integrity of results, the very point of the competition disappears.