I have a player who is heavily into the history and lore of faerun in dungeons and dragons. The problem is that he will use this knowledge to, for lack of a better name, metagame the campaign. for example in our last session the group was in the yawning portal and he tries to have a conversation with Durnan about the red sashes. This group was never mentioned previously in any of our game sessions. He knows of them because he does read a lot and he’s also gathering information from previous campaigns (he used to be a DM). That is just the most recent example. He also tries to bring in aspects from other campaign saying that his character wouldn’t know these things because he’s connected to another character that he played in another campaign, for example: when we were running the dragon heist campaign we fought some creatures that were also in baldur’s gate decent into Avernus. A Vernice as a campaign that he ran so he knew everything about the creatures, and so he played it off as his character knew people in Avernus that would give him the information to fight the creatures. I don’t want to squash his creativity, but at the same time I don’t want him to ruin the game for everybody else. How would you deal with this situation?

I'd have an honest chat with him. Tell him you know that he know's a lot about Faerun because of his experiences as a DM and player. Tell him you understand it's hard not to metagame when you have all that knowledge. Ask him to try to find ways for his character to gain that knowledge IN GAME. If he knows that demons have particular properties and he wants his character to know that, get his PC to do some research, or find a dark priest or some way to gain it so that it gives the story continuity, and also gives the other players the info too.

Second. Change things. It means more work for you as a DM, but if you swap out a few features of monsters or a city, then that will throw him and force him to find info rather than just use it. The Red Sashes? Never heard of them. In YOUR version of Faerun they're called the Crimson Scarves. If he calls you out on it, just tell him honestly, that in your version, there are no Red Sashes. There may be a similar group by another name, but the Red Sashes never existed, and if he wants to find someone like that, he's going to have to do the leg work.

Thanks, great advice 

Quote from MajorPuddles >>

I'd have an honest chat with him. Tell him you know that he know's a lot about Faerun because of his experiences as a DM and player. Tell him you understand it's hard not to metagame when you have all that knowledge. Ask him to try to find ways for his character to gain that knowledge IN GAME. If he knows that demons have particular properties and he wants his character to know that, get his PC to do some research, or find a dark priest or some way to gain it so that it gives the story continuity, and also gives the other players the info too.

Second. Change things. It means more work for you as a DM, but if you swap out a few features of monsters or a city, then that will throw him and force him to find info rather than just use it. The Red Sashes? Never heard of them. In YOUR version of Faerun they're called the Crimson Scarves. If he calls you out on it, just tell him honestly, that in your version, there are no Red Sashes. There may be a similar group by another name, but the Red Sashes never existed, and if he wants to find someone like that, he's going to have to do the leg work.

Good advice on both parts. It's my opinion that if both people have good intentions and open dialogue, most problems or misunderstandings can be worked out with good ol' fashion communication... it's also very fair play to point out that your world / adventures can be based on general info from sourcebooks, but those serve a foundational for inspiration only and your world / adventure can and will have different details to support; and make sure the player Knows this. Plus, if your details / history etc. are different, your player can get the added-on fun of acrually being surprised from time to time.

This is why nothing in my world matches other stories. Monsters are always different. Just keeps it fresh and confuses the players with a lot of knowledge. 

For example any dragon can be good. Had players run into a white dragon that was very kind to them. Traditionally they are quite evil. Also have a very dumb but friendly beholder in the game. Stuff like that throws the players off their game.

Tough situation.  I think the best thing to do with the player is to have a conversation with them.  I certainly empathize; sometimes I have a problem myself separating player knowledge from character knowledge.  I don't do it deliberately, but sometimes it creeps in.  if my DM gives me a gentle reminder I try to do a better job of asking myself "I know this, but does my character".  This popped up recently; my group was running a side campaign (DM travels a lot) doing the ADL modules for avernus in Baldur's Gate.  I know the story of the Hellriders, Elturel and Zariel's fall.  It was relevant information to what we were trying to do.  My character's from Baldur's gate, so I asked the DM, would I know this tale?  He said sure, so I filled in the group as to what went down.

That's what I'd recommend you do with your player.  Tell him why you have concerns and ask him to ask YOU if his character would know that.  If his backstory contains information about people who've been to avernus, then sure he might know that.  If he doesn't have a reason to know people form Avernus, then...he doesn't.  If you don't /care/ if he knows something or it's random lore unrelated to what you're trying to do, let him make a history check.  With your Red Sashes as an example, since they never came up, ask him to make a history check.  If he fails, just tell him your character's never heard of the Red Sashes, or the information he's heard is incorrect.  If he passes, let him know the information and feel like a realms rockstar.

Great instincts here. Good advice. I would flat out say to the player "There is no way your character would be able to know that." Its reasonable to say as a DM that the knowledge they are saying is secreted away in an almost inaccessible place, or that it simply cannot be found or known randomly (Like the identity of secret leader of the Red Sashes for example). Unearthing the deepest secrets of the multiverse can require an adventure or even a whole campaign to do. You could have them roll a history or arcana check and on a really really good role maybe they know something very minor about it. "Like that the red sashes have a secret leader somewhere in Waterdeep". But nothing as specific as their identity, place of business, where they life, etc. Perhaps if they have a convincing backstory you could allow it (like if they were part of the Red Sashes and know the leadership). It is really tempting to delve deep into the lore of such a sell defined fantasy world. But its not really roleplaying anymore if you are using something you found in "The Grand History of the Realms" or some real world lore book as unjustified character knowledge.  Its like knowing the secret magical password to open a magic treasure chest just because you played that adventure before with a different group. 

I always love to play an NPC counter to stereotypes.

A peacfull Orc can make for a great NPC.  Especially if you do voices and choose to go with something good.

All great advice. Thanks. I’m going to implement most of the suggestions here. It’s gotten to the point where other players are now calling him out and I’ve had to jump in and de escalate the situation.

This is one reason I prefer to homebrew as much as possible. Yes, you know how Kobolds are done in the Forgotten Realms, but this is MY world and they work differently here.

Up to and including, maybe Kobolds have Orc stats and Orcs have Kobold stats. My players can't assume that the stats in the MM are the stats in my world. (Sometimes they are, but plenty of times, not.)

For experienced players I allow them to roll a nature or history check to see if they would know specifics about areas or monsters. New players are easy since they don't know anything and can't meta but for experienced players it can be frustrating to not use that knowledge. Allowing a change to use their knowledge seems fair and since their characters were born and raised there, it would make sense they may have some passing knowledge of just about anything there. The more obscure the information they know then the higher the DC.

I reckon base what he knows on his characters int, wis and his background.

Quote from Cage2099 >>

All great advice. Thanks. I’m going to implement most of the suggestions here. It’s gotten to the point where other players are now calling him out and I’ve had to jump in and de escalate the situation.

 If the other players are calling him on it, you definitely have to nip that in the bud.

When you talk to your player and ask them to reign in the meta-abuse, consider challenging them to use that knowledge to further RP and world building. Pick some subjects that their character would know, and if those subjects come up let them run with it. I had a player that had the soldier background and had read a ton of FR lore over the years, from previous editions and novels. I encouraged him at various times, whether in a tavern or at camp, to RP some lore into the game through his character. Gave him a chance to share his D&D knowledge, and there were a couple times when some of his lore made it into my campaign as a plot hook. 

But definitely try to get a handle on the meta-knowledge as stated above. Just recommending an olive branch you can throw so that your player doesn't feel too shut down. 

A conversation I had with my players is that “player knowledge” and “character knowledge” are two entirely different things. This works both ways, if a player thinks their character would know something that they know nothing about, they roll a check against a DC and you tell them what they know. It works the same about something they know lots about.

your players character might have contacts that gave him information on something, but if he fails an Arcana/History/Nature check then he is being let down by his memory of that information.