Sideboard Clearing in Magic: The Gathering
Within the card game Magic: The Gathering, players construct decks with specific themes to duel opponents. These themes fall into three major categories: aggressive, control, and combination, each dictating a style of play and form of win condition. Each style has its strengths and weaknesses. For example, aggressive decks attempt to win as quickly as possible, overwhelming other decks which need time to set up. The strategy can be combated by damage prevention through blocking or “counter” spells. However, not every deck has the resources to stymie an opponent’s strategy. How does one answer an opponent’s strategy if the necessary cards aren’t in one’s deck?
As described by Reid Duke in his article, “The Sideboard”, in tournament play, players have a sideboard, a small set of cards outside the main deck, available to them. Between games in a multigame match, players have the opportunity to exchange cards in their main deck and their sideboard. The purpose of the sideboard is to enable players to optimize their decks to fight their opponent’s. Unfortunately, there is limited space within these sideboards (typically 15 cards), so before tournaments, players will have to choose which cards to include.
There is a tradeoff to including any card within the sideboard. Certain cards placate certain strategies but have no effect on others. The value of a card is determined by the opponent’s strategy, although, these values are not constant between matches, as each new opponent may employ a different playstyle. Before a tournament, one has to determine the likelihood of facing each known strategy and optimize one’s sideboard accordingly.
Of the plethora of cards available, only certain combinations will form effective sideboard options. If one considers the cards to be buyers in a market for 15 slots, then the valuation of each buyer for a slot is equal to the value of incorporating that card to deal with expected opposing strategies. With an objective of social-welfare maximization, one can form a set of “tournament-clearing” options for one’s sideboard. Optimizing “tournament clearing” options is beneficial for players, as it will increase their probability of winning a match against any known strategy.
https://magic.wizards.com/en/articles/archive/level-one/sideboard-2015-08-10