- The "ko" rule in Go exists purely to prevent infinite loops.
- Additionally, in Chinese Go, the "superko" rule is there to patch out all the other very rare repeated positions the normal ko rule misses. When the board repeats without the ko rule being violated in Japanese go, the game ends in a "no result" (with the komi rule below, this is the only way a draw can happen). This is very rare because usually one of the players will be willing to give up control of the area to score elsewhere.
- The komi rule: Since black moves first, it often begins with sente, where the player makes a series of moves the opponent must defend against. The rule gives white somewhere between a 4.5 and 7.5 point advantage in most tournaments. When the percentage of black wins rises significantly above 50% in tournaments, the amount of komi is adjusted to keep things even.
- In previous rulesets, the objective in Arimaa is to move one rabbit to the opponent's home row or prevent the opponent from making a valid move. Some players decided that they were much better than the AI and sacrificed all their rabbits before winning the game without any pieces on the board. Later rules added a change, where you win if your opponent no longer has rabbits.
- Chess has several examples:
- A major rule change in chess was allowing a pawn to move two squares on its first move. It was soon noticed that this allowed a pawn to "slip past" an enemy pawn which would otherwise have been able to capture it, potentially resulting in long chains of mutually blockaded pawns. Since the two-square rule was only meant to make the game faster and not to alter strategy, the en passant rule was introduced to patch the hole: if a pawn slips past another like this, the opposing pawn is allowed one chance to capture it on the square that it skipped over. The threat is greater than the execution; players tend to avoid the two-square initial move rather than allow an en passant capture. Unavoidably, the two-square rule has changed chess, but en passant has helped to limit its effect.
- Chess does not out-and-out ban infinite loops like Go, but either player has the option of declaring the game a draw if the same position occurs three times with the same person to play, and the game is an automatic draw if the same position occurs five times.
- More complex loops are prevented by the 50-move and 75-move rules: a game may be declared drawn by either player if 50 moves pass without a pawn being moved or a piece captured (these, being irreversible, are the key signs of progress in a game), and is an automatic draw after 75 such moves.
- The 50-move rule was once subjected to a really obvious rule patch. It was discovered that certain positions can be won but require more than fifty moves (without captures or pawn moves) to do so. To take care of this, the rules were changed to list these positions and specifically exclude them from the 50-move rule, allowing players to win the game in such positions instead of drawing. This was abolished in 1992, because it was found that there were far too many such positions to continue patching the rules like this, so it was declared that if you ended up in such a position, it was your own fault.
- One popular myth states that the rules were at some point updated to say that a King and Rook had to be in the same rank to castle. This is normally how it's done, but as the story goes, someone created a joke puzzle (requiring the king and rook to castle vertically, which could only be done if you promoted a pawn to a rook and then noted that the resulting rook had not moved before and was thus eligible to castle) to show that the loophole existed. While the joke puzzle exists, the loophole never did; the first version of the FIDE Laws from 1930 already stated that a King and Rook had to be in the same rank to castle.
- A player can cause checkmate by advancing a pawn to the final rank and promoting it to a piece of the other player's color. The opponent then can no longer escape checkmate by having their king capture said piece. The rules have since prohibited changing a piece's color upon promotion.
- Check was once defined as the King being under attack from one or two of the opponent's pieces. The latter is called double check, and occurs when a piece moves to attack the King, while also moving out of the way of an attack from another piece. The laws also require that a player in check should get out of it on the immediately next move (being unable to do so is checkmate). This forces the player to move the King, because it is impossible to move any other piece to block both checks or capture both attacking pieces at once. That was until Robert Norman posted a different plan to the CHESS magazine: move a piece to expose your King to another check. Since the King is now under attack from three pieces, you are technically not in check any more. The wording was then changed to one or more.
- It is said that time limits in formal chess games were introduced after an opponent drove 19th-century grandmaster Paul Morphy to frustration by taking several hours on one move.
- The king is not allowed to be moved to or through a square that is under attack by an opponent's piece. The only situation where the "or through" part of this rule would come into play is during a castling move, which could theoretically move the king out of a situation which would be checkmate on any other square.
- Xiangqi (Chinese chess) is less forgiving of perpetual checks than Western chess. If you check five turns in a row without pause, whether the position is repeated or not, you lose the game. However, in Xiangqi, the general's movement is limited to a small area called the palace, so if you really can't figure out how to checkmate him, you deserve the loss.
- In Shōgi, almost all games end in checkmate. However, there's a situation which was not originally thought of where it can be impossible for either side to achieve a checkmate if both kings enter the opposing side's promotion ranks. This is called "entering king", and is regarded as one of the only possibilities for a stalemate. If such a position arises, arbitrary rules on counting the amount of pieces 'owned' by each side and assigning a point value to them were created. If either side has less than 24 points, then they lose. If both sides have enough points, then the game is simply replayed over again with the starting move switched to the other player.
- Another situation arrived in professional shogi matches. The rule used to be that if a player caused a repetition of moves three times in a row, the game would be considered a draw. (This would happen through one player dropping a piece, a sacrifice occurring, and then an endless cycle of sacrificing and replacing the same piece.) However, one shogi professional found that he could avoid this rule by switching the type of piece he played every other move, so that the repetition did not occur three times in a row. Under those rules, there was nothing that could be done and play continued with the same moves being made until the defending player finally got fed up and tried something else, allowing the instigator to go on and win. The rules were hastily changed so that if an exact same board position (including pieces in hand) happens four times, regardless of sequence, then it's an automatic draw. (Note that this is different from perpetual check, which results in an auto-loss for the instigator.)
- In Japanese Mahjong, players need at least 1 yaku to win a hand. The All simples (Tanyao) yaku is particularly easy to get with open (containing called discards from other players) hands. This has caused many players to call tiles left and right in order to finish their hand with Tanyao as their only yaku for a pitiful point value, much to the annoyance of any opponents denied a bigger scoring opportunity as a result. This has led to a controversial House Rule known as "kuitan nashi" which only allows Tanyao on closed hands.
- Another one is the agari yame House Rule. Normally, if the dealer wins a hand, an extra hand is played which does not count towards the total number of hands in the match, and the dealer keeps the dealer button for the extra hand(s). With the agari yame rule in effect, the extra hand is not triggered if the dealer wins on the last hand and they are in first place. This is to prevent a Springtime for Hitler scenario - in the Japanese variant, it is not uncommon for the player who ends in first place to receive a large bonus (of ranking points in league or tournament play, or cash in gambling play). Thus, on the final hand without agari yame, if the dealer is in first place, they might be better off not winning the hand to end the game and secure their first-place finish, while winning the hand would trigger an extra hand, during which they would have to risk being knocked out of first.
- The Finnish board game Star of Africa had a small flaw in the original rules - the game could become unwinnable for one or more players because of the cost of travelling by sea and the possibility of getting robbed or finding the titular diamond on one of the islands. After 50 years of unwinnable games and House Rules, the sea travel was patched to resolve the formerly unwinnable situations by making sea travel free if the player has no money but only 2 spaces at a time.
- The Battlestar Galactica board game has had a few. In the base game, the secrecy rules were essentially a patch for the core mechanics, since the game breaks if players are allowed to openly discuss their card plays. The first expansion included replacements for a particular skill card to fix a degenerate human strategy, and an overlay for certain spaces of the board to fix a degenerate Cylon strategy. It also introduced an execution mechanic, which revealed the loyalty of the executed player, who would then 'respawn' as someone else. But their loyalty didn't change, which meant that human players began willingly jumping out of the airlock to prove themselves. This was patched in the next expansion by making executed players draw another loyalty card.
- Later releases of Arkham Horror, as well as later versions of the rulebook included with some expansions, explicitly ban certain cards and/or types of cards from being the initial draw. The effects of the banned cards could easily render an already deviously difficult game impossible to win before the players had even taken a single turn.
- The first expansion to the Game Of Thrones board game, and the subsequent second edition, added ports to some territories to bar a common strategy where Greyjoy would scuttle the Lannister fleet and bottle up Lannisport on the first turn, more or less denying them the sea for the remainder of the game.
- In Scythe, the Rusviet Union and Industrial is the only Faction & Player Mat combo that is specifically outlawed by the FAQ. The Rusviet's "Relentless" ability (ignore the "no identical actions on successive turns" rule) has the potential to let them exploit the oil reserve next to their starting space to let them quickly acquire more workers and the Mech Speed upgrade on the Industrial mat can give the faction 4 of the 6 stars they need in record time and with little chance for reprisal.
- The combo of Crimean Khanate and Patriotic has also been banned. Like Rusviet/Industrial, an experienced player can win in 14 turns, well below the average of 18-22.
- Res Arcana: The Ancient Dragon, a particularly expensive dragon in the Perlae Imperii Expansion Pack, says that it can't be placed by Dragon Teethnote or discarded with Sacrificial Dagger.note
Obvious Rule Patch / Board Games