History Main / ThatOneRule

** In third edition [=DnD=], (and, by extension ''TabletopGame/{{Pathfinder}}'') most [=DMs=] just have monsters and [=NPCs=] die when they reach 0 hp or lower rather than tracking their hp (the rules officially state that characters don't die till they reach -10 hp or the negative of whatever their constitution score is in Pathfinder), mainly because it is both a hassle and creates some moral quandaries, as killing an opponent who is already unconscious and bleeding to death doesn't seem very heroic. The big exception being monsters in Pathfinder with the Ferocity ability (which lets them [[TheDeterminator remain conscious and keep fighting till they are reduced to negative con hp]]).
*** Pathfinder second edition (which removes negative hp and just has a character fall unconscious and have to make saving throws to avoid dying) explicitly says that monsters and [=NPCs=] should just die when brought to 0 hp, unless it was due to a non-lethal attack.
*** Fifth Edition doesn't have "nonlethal" damage as a rule at all. Instead, whoever deals the damage which reduces a creature to zero HP can simply declare they are knocking their target out rather than killing them. Of course, this is still subject to DM arbitration as to whether this is possible given the ''way'' the damage was dealt. It's certainly possible to knock somebody out with a TapOnTheHead; knocking them out with a Fireball is a little more dicey.

** Before 4th edition, initiating a grappling attack was usually cause for your entire gaming group to throw large, heavy objects at you. There's a reason the trope is called GrapplingWithGrapplingRules. Even in later editions where it's been simplified, expect the DM to have to go look the rules up to actually resolve your attack.

** Attacks of Opportunity/Opportunity Attacks started out like this in Third Edition, so each successive edition of the game has mostly scaled them back. The basic principle behind them was simple and understandable: In a game that uses turns for simplicity instead of real-time, there should be some kind of restriction against a character abusing the turn-based rules to simply bypass a whole group of defenders to take out a weaker target, steal an object, etc. The problems occurred with both confusing terminology and an "everything but the kitchen sink" approach as more situations were added to what could trigger an Opportunity Attack. The former described this as a situation where the trigger creature lowers their defenses, but a more accurate description would be a situation where the trigger creature lowers their counter-attack offense: i.e., you can take a free swing at them because you're not worried about leaving an opening for them to swing back at you. The latter issue combines with the first issue confusion to where using an action triggers an attack even though the condition where the action was made isn't changing regardless of the action. To explain, why does attempting to stand up from prone trigger a free attack but simply lying helplessly prone does not, or attacking someone without a melee weapon in hand (e.g., crossbow or punching) triggers an [=AoO=] but simply standing there unarmed doesn't?
*** Fourth Edition reduced the circumstances to just attempting to move past a creature or use a ranged attack next to them, although oddly giving the defender supposedly unlimited attacks as long as it was against a new target, and Fifth Edition reduced this even further to just moving past the defending creature completely, as you can still circle around an opponent. No edition has brought up the concept of removing your ability to use [=AoO=] if other enemies are engaging you (e.g. if you have five creatures engaging you, how can you possibly get a free swing at a different one?), but most likely is due to the rules getting just too complex at that point.

*** Since castling is common and therefore learned early, most instances of confusion come in the form of people assuming additional rules that don't actually exist. More than one master-level player has had to ask a judge mid-game if they could castle when their rook is under attack (You can).

'''Alan:''' She's got it!

** A few old-school cards have very complex rulings because they were made before making sure that there was no room for interpretation became one of the game's priorities. See for example [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=202494 Ice Cauldron]] or [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=202591 Word of Command.]] However, the absolute worst part of the rules is what happens when there are multiple persistent abilities that affect what a card can do, epitomized by the interaction between [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=397614 Humility]] and [[http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=15142 Opalescence.]] Witness the block of rule clarification on the interaction between those two cards specifically, as well as how many times those rulings have changed.

** In Creator/RobertAsprin's ''Literature/PhulesCompany'', during the fencing match between [[EliteArmy the Red Eagles]] and the [[RagtagBunchOfMisfits Omega Company]], Phule gives a brief explanation of right-of-way to the audience prior to the beginning of the match. They are okay with it during the foil bout. confused and angry about it during the sabre bout because the Omega Company fencer loses points to it all the time (he's not a fencer at all, but an escrima fighter, and he's clearly landing attacks that would work in a real fight, but violate right-of-way), and when he announces the epee bout, they cheer when he tells them that epee doesn't use right-of-way at all.

** In Stephen Baxter's ''Time's Eye'', British soldiers from colonial-era India try to explain cricket to the army of Alexander the Great. They manage to get most of it across with gestures and broken Greek. They give up trying to explain Leg Before Wicket.
** In WebSite/SFDebris' review of the ''Series/StarTrekVoyager'' episode "Persistence of Vision", a vision of his disapproving father asks Tom Paris several difficult trivia questions, which Tom successfully answers, until he asks him to explain the Leg Before Wicket rule, which Tom fails to do, causing the vision to dismiss him as useless.

** The last time Banding was printed on a physical card was back in the 90's, and for good reason. It's widely considered the strangest and most unintuitive mechanic in Magic's long history. The basic concept is fairly simple: When attacking or blocking, your creatures can form "bands", which are effectively treated as one creature in combat from then on. All but one creature in an attacking band must have banding, and at least one creature in a defending band must have Banding, which is already strange, but tons of other questions also come up as soon as combat happens, such as: what abilities the band will or won't have, how damage from and against the band actually works, how the opponents creatures and abilities interact with their banded creature and so on. And this is without even getting into the "Bands with Other", a more specific subtype of banding with an additional restriction on what could be in the band (for example, "Bands with Other Wolves"). It used to be even worse, as well, because prior to a 2010 rules update creatures with "Bands with Other" ability could only band with other creatures that also had the same "Bands with Other" ability, not any creature that met the condition.

** In 5E, the Challenge Rating system is intended to help the DM balance encounters, but is infamous for how bad it is at doing so. The Challenge Rating/CR of a monster is designed to tell you how great a threat the monster is by saying that four adventurers of the monster's CR should have a difficult but winnable fight. For example, if a monster's CR is 3, that means four party members, each of whom are at level 3, should find such a beast to be a worthy challenge, but not a deadly one. Trouble is, what counts as worthy of a high CR is completely arbitrary, self-contradictory, and hard to pin down. One monster with a CR of 10 may be surprisingly easy for a party of level 6 characters, while a monster with a CR of 12 may end up causing a TotalPartyKill on a level 15 party. Plus, even though the adventurers can only reach level 20, a monster's CR can go as high as 30, which is where the system gets really arbitrary, as in order for a monster to have a total CR of 30 its offensive and defensive statistics must both be above certain values, with there being technically no cap. What is not generally obvious but has been claimed by MCDMs analysis is that a single CR30 monster accounts to roughly half of the daily budget over a 2-short rest adventuring day for a party of 4-6 level 20 characters. While the Dungeon Masters Guides pages on calculating CR work wonders for homebrewers and Xanathars Guide To Everything contains yet more tables on quickly creating encounters, none of the books after the core rules have bothered to explain the value of specific abilities and next to no homebrewers have done so, requiring enterprising DMs to reverse-engineer the CR of monsters so they can use their abilities in other monsters.

*** Since castling is common and therefore learned early, most instances of confusion come in the form of people assuming assuming additional rules that don't actually exist. More than one master-level player has had to ask a judge mid-game if they could castle when their rook is under attack (You can).