When playing D&D, I have always taken the following approach:

• I will do my best to adhere to Rules As Written (RAW)


• If I don't know a rule off the top of my head I will look it up


• If something I say conflicts with RAW, I will look at the rule and reevaluate my decision


• If RAW is not clear I will make a ruling

For the most part this has worked well for me, but I have found that certain players (while agreeing to this initially) are not happy.

What has been happening to me lately is that when I make a ruling and certain people are not happy with that ruling, they will basically stop playing to start googling for arguments to support how they thought the rule should have worked.

Sometimes this ends up coming back to this website, or Sage Advice, or even a random reddit post. The point, once this player finds someone online who agrees with them, an argument ensues about how that rule should be applied. I have been trying to explain to this person that Sage Advice, and similar posts are giving him a Rules As Interpreted (RAI) approach and in my attempt to use the RAW, I do not see it that way. This usually ends with this person getting upset and put out.

It has gotten to the point where they come with web sources prepped and just spring them on me mid-game, only to be upset if I don't agree. It seems like the player is almost trying to set up a "gotcha" moment where they are right and I am wrong. If they spent more time talking to me about specific rules they are trying to "loophole" I might be able to help them and talk about it before the session, but it really feels like this person wants to be seen as right in front of the group and by springing these interpretations mid game, I won't be able to disagree.

All I want to do is run a game where everyone has fun, and we aren't constantly at odds about the rules.

How can I maintain my approach to the rules and find a way for this person to have fun without letting them walk all over any ruling I make?

Agree as a table that rules discussions happen out-of-session

We have had this issue at our table. Rules debates that have gotten out of hand and players looking up rules and rulings disrupting the session. The following method is what helped our issue a lot:

1. If any rule is unclear or confusing the DM will make a quick, temporary ruling
   during the session (that is binding only for that session). Usually, I rule in
   favor of the player especially in cases where it is life or death. But at your table you can use
   whatever criteria allows you to make a quick decisive ruling that seems fair. Do not allow any argument about this ruling at the table.




2. Either after this session or before the next one, I will review the
   ruling, I'll look at the rules, talk with the player and hear their
   arguments and come to a final decision about how the rule will work
   going forward. This ruling is considered final.

At some point before a session, let your players know that this will be the way you handle rules disputes going forward. You will not accept any debate during the session but make it clear that you are happy to talk with them before or after. Try to make it clear why you are ruling this way too: rules debate breaks up the story that your group is trying to craft. This rules keeps the fun session going while allowing rules to be addressed at a later time. Ask them to trust you as a DM and to allow you to make a ruling that seems fair and quick in order to keep things fun for everyone. Talk about it and get buy-in from everyone at the table.

The key thing here is to make a quick ruling at the table (but make it as fair as you can) that is considered to be a temporary ruling until you can think about it more and evaluate the evidence which must happen out of session. Explain to your players that you will not be hearing any arguments about this ruling until the session ends and that there is no point to looking up stuff now. Play the game with my ruling now, and we can talk about the ruling later.

As a DM you may want to be a bit lenient here with the temporary ruling depending on how sure of your ruling you are. If a "wrong" ruling on your part causes a PC death or causes BBEG to escape where they would have been defeated, then it can create sore feelings. I tend to rule in favor of the players most of the time unless they are very obviously incorrect and it has an obvious negative impact on the game.

An interesting byproduct of this ruling is that players often bring up questions they have for rulings before session since they know they can't debate during. This is great for both of us as we can go into the session with an agreed upon ruling (even if I end up disagreeing with the player). Obviously though, this won't work for everything as rules issues are often unexpected.

In our games implementing this method has vastly cut down in the amount of rules arguing and has improved flow and fun for the whole table. We've played this way under multiple DMs (not just me) and I've also done this as a player. It has worked effectively in each situation.

Declare last call for arguments/issues before the session begins

One specific technique that I have not tested, but seems like it would help in your circumstance was suggested by @philbo in a comment: Simply stop before every session and ask if the players have any rules issues or other topics they wish to discuss before you begin the session.

Explicitly state that this includes any rules arguments that people anticipate. After that, the player is going to look pretty silly trying to spring a pre-planned rules argument mid-session on you and you can simply respond: "I gave you the chance to bring this up at the beginning of the session and you chose not to. Now you have to wait until the end and then we can discuss it."

What if players keep trying to argue during the session?

Once you have made it clear how and when rules debates happen, do not engage in debate. If they start to argue, tell them "I made my ruling, see me after the session and we will talk." If they keep arguing, for example during combat, tell them that if they do not move past it and choose something you will skip their turn.

If you remain firm on the point and don't engage at all, players will soon learn that it is no good to try to argue during the session. At my table, players learned this very quickly and I didn't have to invoke it more than a handful of times.

You have the final say as a DM

It is also probably worth it to remind your players that you as the DM have the final say on rulings at the table and how the rules are interpreted. Remember, there are often multiple ways to read the RAW and it is not some monolithic "correct" ruling that is clear. Sometimes the RAW is unclear or even silent on an issue. Sometimes this is even by design since 5e is designed to be less focused on detailed interactions instead trusting the DM to make the ruling they think will be best for their table.

In the end, tell them that you will always be focused on making things fair and fun, but when you make a decision final you consider it to be done unless new issues crop up. In the end, it is your decision that matters for the table, not Google's, not Jeremy Crawford's¹ and not RPG.se's.

^{1 - You also might find it helpful to note that you are correct in your stance on designer clarifications. They are not RAW (though they might be a RAW interpretation). And they are often expressing how the game is intended to be run. None of which has any binding impact on how you rule at your table. Note also that Crawford tweets are now explicitly unofficial rulings.}

Establish a group at-table norm: we are here to play, not to argue

You need to address this before the next session starts, and get buy in from the whole table. Discuss rules before and after the session, but once you hit "play" rules discussion/argument are not part of the play.

Some people get a lot of enjoyment in discussing and arguing about the rules. (Hence sites like this one). But not everyone does, and some people just want to play. Your other players' play experience is being encroached upon by this player's approach.

Get buy in from the whole table and don't begin until all agree. You need the support of the other players in this. Yes, this is called peer pressure, and it is a positive form of that.

You can also take this a step further and develop an at table dispute resolution tool if your table needs that. I outlined one here a while back that you may find useful. (Our table finds that approach healthy and helpful).

An agreed verbal cue can be a useful tool

Our verbal trigger for any in-play question on a ruling is I thought it worked like this {say how one thinks it works} Can be used once for a given situation. This verbal cue allows a DM to catch and correct a mistake, to make or revise a ruling, and then play on. Or, to say, "it works like this" and play on.

As above, a tool or technique like this needs to be settled and agreed upon by the whole group in order for it to be effective.

The top-voted answers are very good. I'd like to highlight one thing in particular in your current protocol, bullet point #2:

If I don't know a rule off the top of my head I will look it up

I will suggest that this is a mistake, and is the first step that puts you on this path of "challenging" DM rulings in-game. Consider trying to run a game with the exact opposite philosophy; try to commit to no book-lookups by the DM at all during the game. Stuff in immediate sight on the DM screen can be acceptable. Rulings can be revisited after the game, and possible resolutions might be: (1) practice remembering that rule better, (2) add it to the DM screen, (3) document a house-rule that your discovered way seems better.

This is sort of an old-school sensibility that makes the game flow much faster.

Good points in the answers so far. Let me add one more.

Both you and the players build a mental picture of a fictional universe.

This universe contains both "physical" and "magical" laws, some similar to the real world and some different. It also contains both published geography, history, and people and those developed for/through your game. Building an universe is fun. Understanding an universe is important for gameplay because it gives the players agency, the ability to let their characters act in the universe with a realistic option of success.

• In the real world, if you stand in next to a small creek you have some idea if you can jump across. You might underestimate how slippery the other bank is, or you might have little experience in jumping with a hiking pack, or you suddenly notice that you're no longer 16 years old. Still, you have some idea.


• Even without personal experience (I hope), you will have some idea how much damage a pistol bullet will do to a human. Your information will be less certain than in the jump example, and as a gamer you will be aware that the concept of a "critical hit" translates to reality. A hit to the arm might go through the muscle, or shatter a bone, or sever a major blood vessel. Still, you have some idea.


• A rogue character will have some idea if he or she can climb a castle wall. He or she has done it countless times. Again, there are risks. The stones might be more slippery than they look. It might be impossible to get a dagger into the cracks. But he or she has some idea what will happen. The player of the rogue gets an idea what will happen by studying the rules. "I would have to roll a crit to fail at this."


• A barbarian hero character will have some idea if he or she can defeat a non-player character. The barbarian looks how the NPC grips the sword, if the eyes dart around or are steady, if the armor looks well-cared-for or ill-fitting. Again, plenty of risks. But he or she has some idea what will happen. The player of the barbarian gets an idea by studying the rules. "If this is the usual mook castle guard, I will defeat him and stay unharmed."
  

Rules knowledge is much less intuitive than real-world knowledge, but it can give the exact odds if all modifiers and rules are known.

Players are trying to make their characters do impressive feats.

In this, they are in a contest with the GM ("our party defeated the Boss Monster") and with each other ("my ranger defeated the Boss Monster"). As the game goes on, they are constantly evaluating their options. They want to feel good because their character did well against the challenges of the fictional world.

As pointed out above, doing this requires the players to understand the fictional universe.

Imagine that you have an important exam in the real world. You study, you worry, you go there and you think you aced the exam, but as you hand it in the teacher says "hmm, I see you used a fountain pen. Didn't you know that you must use a pencil?" Some stupid little rule you didn't know. Or worse, a rule you did know, now that it is mentioned, but which you forgot.

That's how players feel, time and again, if they made a plan for their character and the rules (and world) interpretation of the GM makes it fail. But that's what will happen, because the players' knowledge of their fictional world doesn't come close to their knowledge of the real world.

If the players are uncertain about the fictional world, they may come prepared to argue the world interpretation on which they have staked the actions of their players. If they are certain some approach won't work, they are less likely to select that course of action to start with.

A partial solution:

Talk to your players about how you interpret the rules outside game time. In abstract, without reference to the specific characters. "Do you think a Cleric can ...?" and so on. Involve them in creating the history and geography of the world. This gives a "common operational picture" of the world. As a GM, you are still required to have secrets and surprises, but the world is something you share with the players.