Kingmaker scenario

A kingmaker scenario, in a game of three or more players, is an endgame situation where a player unable to win (see: lame duck) has the capacity to determine which player among others is the winner. Said player is referred to as the "kingmaker" or "spoiler". No longer playing for him- or herself, he or she may make game decisions to favor a player who played more favorably (to him or her) earlier in the game. Except in games where interpersonal politics, by design, play a decisive role, this is undesirable.

In the context of a democratic election, this scenario is termed the spoiler effect.

Gladiator example

Consider this simple game: Three gladiators play, with strengths 3, 4, 5. In turn, each gladiator must "engage" another, and they begin "combat". The result of combat is that the weaker player is eliminated, and the stronger player loses strength equal to that of the weaker player. (For example, if "5" attacks "3", "3" will die and "5" will have strength 2.) The winning gladiator is the last one standing.

The gladiator whose turn is first is the kingmaker. Here's why: Each round of combat eliminates one gladiator, so there will be two rounds of combat. The first round of combat will eliminate one participant and weaken the other to a strength no greater than 2. The nonparticipant's strength is at least 3, so he is guaranteed to win the second round of combat, and the entire contest. Therefore, the game collapses: The winning gladiator is the one not involved in the first battle.

Hence, the gladiator whose turn comes first is the kingmaker. He must be involved in the first battle, hence cannot win, but with the liberty of choosing his opponent in that battle, can elect either of the other two players to be the winner of the contest.

Kingmaker scenarios in practice

Because they allow the outcome of the game to be determined by a player of (presumably) inferior strategy, kingmaker scenarios are usually considered undesirable, though to some extent they may be unavoidable in strategy games. Of course the argument can be made that this means the winner, chosen by the kingmaker played with the additional restriction of not annoying the other players as much, presumably a more difficult task. In these games, the game mechanics, players' outcomes and strategies are often so interconnected that to eliminate all possibilities of this situation is almost impossible.

In tournament situations, kingmaker situations can be especially corrupting, since a losing player may use this power to influence events beyond the scope of the game at hand. For example, if seating in future rounds is dictated by past performance, a losing player in this situation might use his or her position of power to place a weaker player at his or her table in subsequent rounds.

Different games deal with the kingmaker problem in different ways:

* In the group stages of tournaments such as the FIFA world cup, the final set of games in the group are often played at the same time, thus reducing the possibility of a team who will not qualify for the next round being able to sit back and let their opponent win, thus guaranteeing them a place. This rule also stops leaders of the group playing for a draw and guaranteeing that they both go through.

* In the game of Puerto Rico, players conceal their victory point totals by overturning their hexagonal tiles, which could denote either 1 or 5 points. This ambiguity makes it unclear (unless players are especially attentive) which player is in the lead.

* In Monopoly, rules regarding behavior at bankruptcy serve to reduce the frequency of kingmaker situations.

* Most games prohibit---with penalties greater than match loss (for example, ostracization, disqualification)---questionable or unsportsmanlike conduct geared toward effecting a kingmaker scenario.
** Stalling, or intentionally slowing game play in timed games, for personal advantage or to that of a currently leading player, is normally treated as unsportsmanlike conduct.
** The use of revokes, or intentional rules violations, in trick-taking card games, to void a round and effect a kingmaker scenario is discouraged by use of severe penalties. In tournaments, doing this can be classified as cheating.

*In the later rounds of a tournament, the rules permit concessions for any reason other than bribery, and thus a player who is unable to make the top 8 will usually concede when paired with somebody who would be able to make it.

Other games may explicitly encourage a kingmaker scenario. An example of this is the television series Survivor, where the last seven contestants voted out form a jury that chooses a winner from the final two contestants.