Loophole Abuse/Tabletop Games

Board Games

 * Old time wargamers of the Avalon Hill type may remember the nightmarish nonsense—like losing all of the British Empire to an attack carried out on London by a single airborne unit—that followed trying to play Rise and Decline of the Third Reich in its first edition in the mid 1970s. (The game's designer, John Prados, is brilliant at concept but, even in the seventh edition published in 2000, proved that he still can't write rules for doodly.....)
 * Apparently, the official rules of Chess once had a loophole that rendered the game 1.e4 e5 2.Bc4 Nc6 3.Qxf7 mate a victory for White. Although the White Queen cannot move this way legally, checkmate ended the game. The other side could only claim an illegal move while the game was in play. After a checkmate, legal move or not, it was too late. This is just the most famous example of how this major flaw in the rules could be exploited.
 * The current FIDE Laws now state that checkmate ends the game, provided the move that brought it about was legal. Which ends that one.
 * For a while, there was no rule that you couldn't promote a pawn into an enemy piece to block the other player's path.
 * There is a similar case of promoting a pawn into a king.
 * Castling can be performed with a king and a rook which have never moved from the position they were placed. Which led to someone promoting their king's pawn into a rook and using it to castle vertically, until the rules were rewritten to prevent this.
 * Scrabble. It is, technically, perfectly legal to play words that don't exist - you just have to pay the penalty if you're challenged. If you can bluff your opponents into thinking it's a real word and not challenging, you're good to go.
 * An episode of CSI featured a Lawyer-Friendly Cameo Scrabble player who used this as his play style. He would play a fake word (in this example: "exvin") and bluff his opponent (the justifying definition: "a wine aficionado that no longer drinks"). When the opponent extended the word ("exvins"), the first player would call a challenge, at which point the opponent had to pick up all the offending letter tiles in addition to the one he played and take a penalty. The player ended up literally choking on his words.
 * The Lore of Blood Bowl is rife with coaches doing whatever it takes to win. For example, players are strictly forbidden from carrying weapons on the pitch. Where most players figured it didn't count as a weapon if the blades were fixed to the armour, the Dwarves argued it meant riding a bulldozer on the field was allowed - it's not carried, is it? The actual gameplay reflects that spirit. In first and second edition of the game, the rulebooks for the various ways a player could cheat were almost as long as the actual game's rules (and even more byzantine).
 * An in-universe example from Warhammer 40,000. The Ecclesasty cannot have "Men-At-Arms", due to some high mucky-muck trying to take over The Empire. Cue Amazon Brigade. (Whether this was loophole abuse or the reason for the phrasing varies by source).
 * The FAQ articles have had to correct some in the past. The Swooping Hawks' Intercept rule reads "the unit never requires worse than a 4+ to hit an enemy vehicle", which means that the WS 4 Swooping Hawks could hit a WS 5 Venerable Dreadnaught on a 4+ instead of a 5+ as the normal compare-WS table would indicate, for instance. An Ork list that was designed entirely around exploiting the wound allocation rules in fifth edition by giving every model in every unit different gear was briefly popular on the tournament scene.
 * in the Axis & Allies miniatures game, air units were a late addition, meaning a lot of previous cards weren't prepared for their entry. Thus, units that should not be able to attack planes, like mortars and certain assault guns, can. Worst of all, land mines can affect planes. Those are some epically bouncing betties.
 * Errata dictates that units with the "bombardment" ability can no longer attack planes, eliminating most ground artillery from the equation—but mines and mortars are still okay.

Card Games
""That's not the purpose of [Go Up A Level cards], but it's so vile and Munchkinly that we love it too much to say no." Steve Jackson Games, on whether Go Up A Level cards could be used on enemies to provoke monsters that ignore characters below a certain level."
 * There's a reason the comprehensive rules and errata for Magic: The Gathering is hundreds of pages long and reads like a federal tax code. The rule-makers are constantly having to close odd loopholes the players figure out with each new batch of cards and the thousands of possible interactions that open up.
 * One of the most (in)famous examples of Magic rule bending is such: There was a card called the Chaos Orb which had the ability to take out of play any card(s) it landed on after you flipped it in the air. One clever player TORE UP his Chaos Orb and sprinkled the pieces all over his opponent's playing area, thus effectively removing most of those cards from the game. The Tournament judge ruled the maneuver legal, as nowhere did it say the card had to be in one piece.
 * The other loophole was for the opposing player to catch the card in the air then either hold on to it (thus it never landed), or drop it on any card they choose. Errata for the eventually specified that you couldn't interfere.
 * If there was such a ruling (they weren't systematically recorded in those days), it was overturned in 1994 with a Word of God ruling that tearing up the card made it "marked", and you would lose the match for playing with a marked card. You would then be required to replace it with another Chaos Orb before the next round started or you would lose that match for illegally changing your deck configuration. Loophole Abuse cuts both ways.
 * This was subsequently parodied in Magic: Unglued with the card "Chaos Confetti".
 * When used as intended Chaos Orb spawned another loophole: players would spread their cards out over a ludicrously large area so Chaos Orb couldn't touch more than one when it landed, or would lean their cards against things so that it was impossible to land on top of them at all. A ruling has since been made that you can't rearrange your cards after Chaos Orb enters the game; also you must not have your cards stacked or in places where your opponent can't read their name or count them.
 * There are a lot of looping combinations.
 * Then of course there was the infamous pre-alpha version of Time Walk, with the text, "Opponent loses next turn". When it was realised that anyone playing it would cause his opponent to lose the game at the start of his next turn, it was changed to "Take an extra turn after this one".
 * An urban legend claims that in one tournament, a player cast a spell with the effect "Target players loses the game," then pointed at a completely different table and said "That guy.". Of course, you can't do that, even if nothing in the rules state the target must be in the game you're playing. That's not something necessary to state explicitly. You can't cast a Lightning Bolt at a player in another game either, or cast Control Magic on one of his creatures, or Counterspell one of his spells.
 * In the Munchkin card game, some people think you can freely equip and use items you are not legally able to, as long as you don't get caught. As in any game, this is cheating if made on purpose.


 * People holding as many cards as possible in your hand and doing whatever they can to prevent others from noticing that they're holding more than five are cheating. Contrary to what some urban legend claims, it's not legal to cheat in Munchkin.
 * In tournament play, it is not. In tabletop play, it is borderline -- Munchkin policy is that unless a rules violation is noted by someone else at the table at the time it is being committed, it does not exist.
 * Early versions of the Loaded Dice card did not specify that the value you choose to replace that of a die roll had to be between one and six. And there are plenty of cards to abuse this with, like one monster that gets a bonus to its level equal to the roll of one die.
 * There are a lot of infamous combos and infinite loops in Yu-Gi-Oh that result from this. The vast majority of them involves exploitation of the ruling that, except in very rare cases, a monster's effect is "reset" when it is flipped face-down or removed from the field temporarily, allowing you to reuse the same effect multiple times in one turn, with the right setup.
 * Before it was banned, the card Last Turn was the subject of quite a few loopholes, mainly due to the fact that it didn't negate monster effects while it was in use. To wit, when it's activated, both players choose a monster to be on the field (the activator from their field, the opponent from their deck) and battle; whoever has a monster remaining on the field after the battle wins, otherwise it's a tie. Thing is, the monster left on the field doesn't have to be the one the player chose for the battle, and the card doesn't negate monster effects, so if you have a monster on the field that can prevent Special Summons (thus, preventing the opponent from getting out their chosen monster), or one that can summon out a monster when destroyed (thus leaving you with a monster after the battle), you can easily screw over the opponent with it.
 * In the CCG "EVE: The Second Genesis" one of the main ways to gain money (used to play further cards) are location cards. One such location has the effect "When this card comes into play, sacrifice a location". The officially sanctioned loophole around this is to play the card into an uncontrolled region. Because the region is uncontrolled, the location is uncontrolled too and the effect does not activate...

Tabletop RPGs

 * Munchkins in Dungeons & Dragons are worse than Rules Lawyers: some players go for full-blown Loophole Abuse.
 * Players can turn Locate City into a nuclear bomb.
 * Others recovered from infinite damage by drowning themselves. Taken literally, the drowning rules set your hit points to zero, even if they're negative.
 * And then It's Wet Outside lets someone make a heal check to stop drowning.
 * Passing an item hand to hand is a free action (doesn't take up time), so if you line up a few thousand people you can get an object to travel miles in six seconds. Then the last person throws it.
 * You can also have one player stand on another player's shoulders and pick him up as a free action. Then the other player picks him up. Since this is all a free action, there is no time for them to fall, and thus they can fly by repeatedly picking eachother up in midair.
 * Dropping an item is a free action, as well. And if you happen to be fireproof and are standing next to an enemy while carrying, say, 500 Alchemist's Fires... Though the logistics of actually carrying 500 Alchemist's Fires is a bit screwy in and of itself (seriously, you normally only have two hands to drop them from).
 * An Obvious Rule Patch in 3.5 obviates the need to Rule Zero the above examples -- the DM may now, at his discretion, rule that the circumstances of a free action are such that your turn ends immediately after completing it.
 * Dungeons & Dragons never has loopholes. Rule 0 (the DM can change whatever rules necessary) ensures this. Of course, it's completely possible just to get something to work merely by having the moxie to think it up and try it.
 * And in almost all cases results in even more loopholes when amateurs with poor understanding of the rules to begin with try to tamper with them.
 * Perhaps the most true-to-form example of this trope (at least by the alternate name, Ain't No Rule) is that while the state of Dying is explicitly defined in the rules as far as what actions are acceptable, the state of Dead has no restrictions. There literally Ain't No Rule preventing a freshly-killed player from standing up and continuing the fight.
 * Incorrect. The moment of death is mentioned elsewhere in the rules as when the player's soul leaves their body and begins its journey to the Outer Planes, so you are prevented from getting back up and adventuring with the party -- as you are no longer with the party, in the dungeon, or even on the Prime Material plane. You could theoretically continue to adventure as a petitioner on the relevant Outer Plane, but that's been true anyway ever since Planescape was published.
 * Additionally, by the rules as written becoming a petitioner is an automatic transition to NPC status - it takes Rule Zero to allow petitioner PCs.
 * There's no official restriction preventing you from using the spell True Creation to make planet-destroying quantities of antimatter.
 * Besides the obvious (just saying "No,"), a GM could ask "So how many ranks do you have in 'Knowledge: Advanced Physics Not Known In This Universe' and 'Craft: Materials I've Never Heard Of?' anyway? Oh, that's right, zero. The spell fails as your caster can't decide to create something he doesn't know exists. Since the XP cost is paid even if the spell fails, I now need to establish a GP value for priceless antimatter. Huh, seems you didn't have enough XP to cast the spell anyway, so it would fail on that grounds too. You're lucky I'm a stickler for the rules, as they state you can't lose a level for this." Loophole Abuse is equally funny when pushed back in the face of a smarmy Rules Lawyer.
 * The various settings tend to have in-universe cases somewhere in all the history and organizations. For instance, House Jorasco healers are not supposed to treat without payment in money... but there is nothing hindering them from lending the necessary money and then setting a task as repayment in kind for the loan.
 * In universe, the infamous Wish spell. This spell can be cast by high level wizards, or can be granted by a few select creatures (like Djinns), but they should always be met with caution. Too careless wishing can result in getting the exact opposite of what was intended, depending on the maliciousness of the creature and / or the DM. For example, when wishing for a mighty artifact, the caster might grant you the artifact... by teleporting you into the tomb where the artifact is located, in the middle of it's undead guardians.
 * The entire concept of Pledges from Changeling: The Lost practically begs the player to use this trope; as is frequently the case with The Fair Folk, neither the True Fae nor Changeling Pledges recognize any such thing as "the spirit of the agreement." You just have to make very, very sure that you actually know what you're doing.
 * This trope is Mr. Welch's bread and butter, even if the GM doesn't tend to be cooperative. The phrase "even if the rules allow it" and variants thereof appear no less than 47 times throughout the ever-growing list.
 * In Mutant: Undergångens arvtagare a robot-class player or NPC could have drones as an "option". Maximum would be 4 without any penalties for too many options, but drones could have their own options, deliberately so for the sake of being useful, but nothing states they couldn't have drones as well. Cue infinite horde of massively powerful drones! (although rule 0 almost always stops this as it's crazy-powerful.