Personally me and some friends rule magical darkness as a thing that makes you lose your sense of direction, when it's our turn we can roll a d4 and it will depend what way we will be moving North,East,South or West and we will most of the time say we will move our entire movement and have the ability of changing if we nolonger are inside the darkness.

Also depending on how you rule it, the Darkness spell says: Magical darkness spreads from a point you choose within range to fill a 15-foot-radius sphere for the duration. The darkness spreads around corners.
Even though it doesn't say at what kind of speed the darkness spreads but it does spread and doesn't appear immediatly so this can give character inside the info that there is this magical effect affecting the surroundings and not their vision itself. Players can ask the DM about if they noticed the darkness spreading or players with high passive perception can know it immediatly at the DM's choice.

Depending on how your Fighter moved i could see it as a minor form of metagaming, If he moves in a strategic way or changes direction inside multiple times then i would say yes, If the character chooses to just run forward the way they were able to see from before the spell and just uses his speed untill he is out and can see again then i would say it's not really meta gaming. The DM can ask for let's say a perception check, an intellegence check or normal wisdom check to make sure he hasn't lost his sense of direction.

At last i like to say something about the minor forms of metagaming, there are alot of small ways that can unconciously let you make small metagaming moves and that is completely fine but i would not try to search for it or try to be to against all those small mistakes because if you would look back at all the things you've done in d&d then you would come across that everyone makes these small mistakes and making a problem of them is only gonna make the game less enjoyable. The DM is there to make sure no major metagaming becomes a thing and if you find that something was a major metagaming moment and the DM didn't do anything maybe keep it in your notes and mention it after the game.

FWIW, the only time I remember Darkness being depicted was in the Dragonlance novels, which were pretty true to the mechanics as far as identifiable spell casting went.  Darkness was "lights out in the flick of switch" type instantaneous effect.  And hopefully this doesn't metagame spoil whatever your DM is working you through, Vince, but I think the passage I'm remembering was an encounter with a black dragon.

Again, if the DM didn't want them to consider the parameters of the spell, they shouldn't have plopped a circle inscribing the spell on the battle map (reinforcing my if you're playing with a battle map, you're metagaming).  

Darkness, and smoke, etc. do trigger a flinch response if its sudden and the sense of sight is totally deprived, and that movement is a factor in the common disorientation people feel with sudden loss of sight.  I too allow checks to see if a character can maintain their bearing.  Sometimes perceptions or an intelligence or wisdom check, or I'll allow athletics or acrobatics to account for proprioception instead of strictly cerebral deliberation/calculation.  Really anything but CON or CHR.  If one character is disoriented, I'll allow oriented characters to lead physically lead disoriented characters.  I'd also allow for advantage/disadvantage for characters if they're are outside voices providing strong guidance or kibitzing from multiple directions.  

Metagaming will always be a factor in the game, it's up to the DM and the table to decide how much OOC knowledge can be imparted in character action.  I'm curious whether the OP has taken the substance of their complaint to their DM (maybe the point of this post is to use the forum as a grand jury to return with a validating indictment, but I don't think that's what happening here at all).  My guess is the DM may say something to the effect of, "Yeah, I see what you're saying, and you're not wrong.  However, the point of that Darkness spell was only to shape the battle zone and maybe occupy the characters for an action or two, not turn an extended game of blind man's bluff into a kill zone for a TPK.  Do you want a rougher game?  Let me know what you and the other players think together."       

Quote from Vince_Snetterton >>

Quote from MidnightPlat >>

FWIW, the only time I remember Darkness being depicted was in the Dragonlance novels, which were pretty true to the mechanics as far as identifiable spell casting went.  Darkness was "lights out in the flick of switch" type instantaneous effect.  And hopefully this doesn't metagame spoil whatever your DM is working you through, Vince, but I think the passage I'm remembering was an encounter with a black dragon.

Again, if the DM didn't want them to consider the parameters of the spell, they shouldn't have plopped a circle inscribing the spell on the battle map (reinforcing my if you're playing with a battle map, you're metagaming).  

Darkness, and smoke, etc. do trigger a flinch response if its sudden and the sense of sight is totally deprived, and that movement is a factor in the common disorientation people feel with sudden loss of sight.  I too allow checks to see if a character can maintain their bearing.  Sometimes perceptions or an intelligence or wisdom check, or I'll allow athletics or acrobatics to account for proprioception instead of strictly cerebral deliberation/calculation.  Really anything but CON or CHR.  If one character is disoriented, I'll allow oriented characters to lead physically lead disoriented characters.  I'd also allow for advantage/disadvantage for characters if they're are outside voices providing strong guidance or kibitzing from multiple directions.  

Metagaming will always be a factor in the game, it's up to the DM and the table to decide how much OOC knowledge can be imparted in character action.  I'm curious whether the OP has taken the substance of their complaint to their DM (maybe the point of this post is to use the forum as a grand jury to return with a validating indictment, but I don't think that's what happening here at all).  My guess is the DM may say something to the effect of, "Yeah, I see what you're saying, and you're not wrong.  However, the point of that Darkness spell was only to shape the battle zone and maybe occupy the characters for an action or two, not turn an extended game of blind man's bluff into a kill zone for a TPK.  Do you want a rougher game?  Let me know what you and the other players think together."       

 Actually, I PM'ed the DM just before I wrote this initial post. I told him it is a virtually impossible situation to resolve.

I wouldn't say impossible.  If it mattered the DM, it comes down to tool usage.  A battlemat or VTT shouldn't control how you play the game, unless you like how it shapes the game.  If the DM wanted or would want to in the future make "fog of war" type effects truly challenging.  Don't plop the darkness onto the map and instead describe what the characters see, or in this case literally don't see, until the effect is figured out.  But I also don't see how the session broken a crime or a break from how the game is supposed to be played or any other call for serious complaint.  

I see a lot of talk usually about player meta-gaming, mostly at low levels because it's always 'you haven't encountered that! you shouldn't know!"  Well sorry but I've never encountered wolves/cheetahs/lions/bears/red pandas/automatic weapons/tanks/missiles/fighter jets/attack helicopters/jack hammers/strip mining equipment/bulldozers/bridge layers/tunnel borers/on and on and on but you know what? I know about em.  Why is it assumed every adventurer is a country bumpkin that spent his entire life on a farm doing nothing but farm stuff until he suddenly picked up a sword and magically became lvl 1.

Basically this. If you are an adventurer, you should know this stuff unless you specifically are told you don't. If you go out to fight a dragon and curl up into a fetal position the first time they cast a spell because you're just a simple medieval peasant, you simply die and the game ends. Sounds like fun!

At the very least, you can make informed decisions. The fighter saw the origin point of the darkness spell expand outwards because that's how the spell works. It doesn't take a rocket scientist to know you should move away from that origin point, because you know if you stay in the darkness you're going to die. At least if you move around, you have a chance of seeing again.

As for the cleric, if I was a frickin Light cleric and someone told me I didn't know what Darkness was, I'd politely gather my things and leave. Banishing darkness is literally their job. It's like saying you've trained your whole life as a firefighter but when your house caught fire you weren't sure what to do because your house had never caught fire before.

While the presumptuous of innocence is the corner stone of some criminal legal systems, the presumption of ignorance to "combat metagaming" may be a crime against game systems.  Light Clerics combat darkness check.  Just because level 1 Rangers have favored foes, doesn't mean other PC classes lack knowledge of their class's most common antagonist.  Also reasonable to articulate that if a fighter had their wits about them, they may endeavor to move toward the direction the darkness flowed toward, much like someone trying to escape an avalanche, fog, smoke, etc.  It's a reasonable course of action, not really a sign of a broken system or to label "all players" engaged in something I think the OP believes if bad conduct.

Few bits on the whole thing have been explained to death.  It MAY have been meta, however the DM, first off, set it up.  When my players get hit with Darkness, they are told "It goes completely dark"  No icons or images on the map...they couldn't SEE the map, with this condition.  It stays up though, I presume they are all relatively bright and can recall roughly what it looked like before it got dark.  In complete darkness (I have worked in underground sites several times, so I know absolute darkness) there is a difference in open and closed eyes.  It's minor, but it's there.  Blindness would be different.  There's the recognition (aside from the "spreading" description of the effect which is a giveaway)  of it being magical darkness.

Reactions of the Fighter.  Training would tell him that since A: there was a hostile nearby when I suddenly couldn't see, B: said hostile seemed to be working some kind of magic, so C: I need to be in a spot that is NOT where I was when he started the magic, I need to move, if for nothing else, but to provide a moving target.  Escaping the darkness could have been a lucky result of the tactical decision.  (This would be more likely if the circle hadn't appeared on the map)

A Cleric who has the whole kill darkness thing would likely have been shown how to recognize darkness as part of learning the skill.  As opposed to "Here's a skill, but we can't or won't tell you when to use it"  This line of thought could apply to any of their light spells, like Daylight, part of the teaching might be that it was particularly useful against various types of undead.

I can understand how meta-gaming can really crap out a session or even a campaign if it's frequent and glaring.  My own groups grimace when they know meta would really help and/or help them avoid a dangerous situation, but push through.  Our Wizard held back her bigger fire spells, concerned about hurting her allies, when the only one in range had resistance to fire.  She knew, but her character didn't.  They went 2 or 3 levels before it came up in IC talking.  Next fight...BOOOOOF  Meta can suck, but meta knowledge and NOT applying it can be hysterical.

All players have to metagame to a certain extent, because barring extreme dissociation or delusion you are aware that you are playing a game and that the game has rules to be followed.  If a wizard learns a "bonus action" spell, is it metagaming for the player to know they can only cast single action cantrips on the same turn?  I'd say yes, but it's appropriate 'metagaming' that helps the game move faster and feel more natural, otherwise the DM would have to explain the rules in-game.

A second kind of appropriate 'metagaming' is what is being described in the OP.  It is impossible for a PC to have the life experience for all things they should know "naturally" to also be known to the player, so shorthanding some assumptions (like, that a Light Cleric with a specific ability/training that counteracts magical darkness would be able to identify magical darkness, even if they hadn't actually seen it cast as a spell yet) is appropriate as no matter how fleshed out a character, you can't replicate the lifetime of experiences that a real person has that informs their actions.  Likewise, the Fighter might not have seen the darkness spell cast in their lifetime, but it could reasonably be assumed that they are familiar with spells, at least enough to know that some spells have AoEs and those AoEs have limits.

For a real world example, take 3 people (persons A, B, and C) and fast food restaurant X.  Person A worked at restaurant X, and knows that Secret Menu item Y exists and can be ordered from direct experience.  This is like a PC with knowledge of the Darkness spell, or possibly the Cleric with training/abilities that are specifically geared to magical darkness.  Person B never worked at restaurant X, but read an article once about Secret Menu item Y, or saw someone another time order Y, and so they know that in general, if you ask for Y you will get it.  That is like the fighter PC;  they may not have first hand experience with the Darkness spell, but they might have had an experience that informs their actions regarding spells in general.  Person C has never been in restaurant X, nor have they read anything about it, so it would be highly questionable/unbelievable if they were able to order Secret Menu Item Y the first time they visited the restaurant...you might think someone was secretly "whispering into their ear" or their knowledge was coming from "somewhere else", ie "toxic" metagaming in D&D.

A lot of this also depends on the DM correctly describing the situation.  For example, innate spellcasting does not remove verbal components, so the dragon's casting of the spell would have come with some sort of chanting that would be recognizable, possibly, to a spellcaster, or to a PC who understood Draconic.  The spell description also describes the darkness created by the spell as "spreading from a point", so the PCs would have seen the darkness expanding, it wouldn't have just gone black.  There are a lot of cues in an appropriately described encounter that would communicate that 1) this is a spell, and/or 2) this is some sort of magical darkness (as opposed to blindness which would be a true "lights out").

The only "toxic" metagaming is that where the players are truly using OoC knowledge to gain an unfair advantage.  Knowing to run out of range of a spell is not unfair.  Knowing that a dragon is a black dragon is not unfair...knowing that the Young Black Dragon statblock indicates it is weak to INT saves or that its AC is 18, and using that knowledge to your advantage (by say, using only spells with INT saving throws right off the bat, or using a bonus ability to bump a 17 attack roll but not a 13 attack roll) would be considered toxic metagaming, without prior experience with young black dragons or a proven character knowledge of said creatures.

Quote from Vince_Snetterton >>

I will propose a slight tweak to this, and then I want those that suggest I am too harsh to to extrapolate what should happen.

Assume the same conditions, but one. The Darkness is not centred over the middle of the group, but is skewed, so let's say the Fighter will have to deal with 35 feet of Darkness if he moves forward, but only 5 feet if he moves back. How do you adjudicate that?

 Have the fighter roll say a D20 (or whatever die the DM wishes) and that determines the direction he moves. That's what our DM got us to do when the characters were put into darkness.

Sorry, came into this late.

I haven’t read through every word of this thread so this may have already been mentioned, but there seems to be a discussion over how a character could tell the difference between the Darkness spell and the Blindness spell.

For me it’s an easy answer. The Darkness spell just happens, no saves or anything. The Blindness spell requires a failed Con save to take effect. Any table I have ever played at would make the effects of Blindness felt by a character even on a save (e.g. “you feel magic come over you as your vision starts to fade, but you are able to shrug it off”, on a save of course). So if the characters didn’t experience the magic of the Blindness spell making them blind then they would know it must be something else.

I don’t know if this is how it might work RAW or if this is even something specifically covered. But I just wanted to add my experiences in, because recognizing that a magical darkness has enveloped them, a character could easily try to run to (hopefully) get out of it with the player meta-gaming.

Quote from Llew_Llaw >>

Quote from Vince_Snetterton >>

I will propose a slight tweak to this, and then I want those that suggest I am too harsh to to extrapolate what should happen.

Assume the same conditions, but one. The Darkness is not centred over the middle of the group, but is skewed, so let's say the Fighter will have to deal with 35 feet of Darkness if he moves forward, but only 5 feet if he moves back. How do you adjudicate that?

 Have the fighter roll say a D20 (or whatever die the DM wishes) and that determines the direction he moves. That's what our DM got us to do when the characters were put into darkness.

Sorry, came into this late.

 Not really a fan of forcing players to accept such a random action in a situation where their characters arguably know quite a lot, and thus should be able to make a somewhat informed and rational decision. They may not know it's a Darkness spell (though they could certainly conjecture about it) or where the boundaries of the spell's effect are, but they more than likely remember the layout of the room to an extent and should have a good idea of where the dragon was last - meaning they'll at the very least won't want to stumble blindly towards said dragon, unless they were to have some kind of blindsense quality, and probably hope to reach cover if it's available as they try to get out of the dark. 

Quote from iconarising >>

 

The only "toxic" metagaming is that where the players are truly using OoC knowledge to gain an unfair advantage.  Knowing to run out of range of a spell is not unfair.  Knowing that a dragon is a black dragon is not unfair...knowing that the Young Black Dragon statblock indicates it is weak to INT saves or that its AC is 18, and using that knowledge to your advantage (by say, using only spells with INT saving throws right off the bat, or using a bonus ability to bump a 17 attack roll but not a 13 attack roll) would be considered toxic metagaming, without prior experience with young black dragons or a proven character knowledge of said creatures.

 Not disagreeing with your argument in general, but defaulting to Int save spells is fairly sensible. I expect casters to have an inkling about which saves are more commonly high and which more commonly low. There's quite a lot of grey area when it comes to what characters know or might at least have some solid notions about.

Quote from Kotath >>

Quote from Beardsinger >>

Quote from Kotath >>

Quote from Beardsinger >>

Unless the fighter is incredibly dense they know several things;

• They were in battle with a magical creature that can cast spells and has an area of effect breath weapon.
• Their companions are all shouting variations of "I'm blind" or "who turned the lights off?"
• If they don't move they are likely to be breath weaponed to death.
• The way they walked in was free from obstacles so if they retrace their steps back out then they can get out of the area.

It isn't really meta-gaming to act on something that an experienced adventurer would already know to do. They simply turn around and walk back the way they came until they can see again.

 

To be fair, it is a lot harder to walk at all blind. But that is a different question of whether one should try or not equals meta gaming.

 Maybe if you have never done it before, but for anyone with any kind of training or experience it isn't difficult. I can move around my house in complete darkness (black out blinds) without walking into anything. A group of adventurers who are powerful enough to chose to go after a dragon should easily be able to do it.

 

I can in parts of mine, but it is very familiar territory. I am rarely far from a wall and more slow, not normal walking speed.

Yes, it's one thing to know your own lair, so to speak, like the back of your hand.  It's very different to presume the same ability to maneuver in a room you've only seen, going back the example, through the door way.  I mean I can walk from my bed to the bathroom with no need for lights too.  But if I was in say the dressing room of a Target store, there's going to be some banging around as I will be that thing that goes bump in the night.  

I still think as presented there's too much faulted on the players for metagaming their knowledge.  Their actions were shaped by the tools the game was using which plopped a darkness circle over the PC's bottle caps.  Best thing would have been for the DM to disable the map if the DM was as frustrated by metagaming as implied in the OP.    

Quote from MidnightPlat >> 

Yes, it's one thing to know your own lair, so to speak, like the back of your hand.  It's very different to presume the same ability to maneuver in a room you've only seen, going back the example, through the door way.  I mean I can walk from my bed to the bathroom with no need for lights too.  But if I was in say the dressing room of a Target store, there's going to be some banging around as I will be that thing that goes bump in the night.  

I still think as presented there's too much faulted on the players for metagaming their knowledge.  Their actions were shaped by the tools the game was using which plopped a darkness circle over the PC's bottle caps.  Best thing would have been for the DM to disable the map if the DM was as frustrated by metagaming as implied in the OP.    

 The point is also that, metagame knowledge or no, those PCs were always going to do something. And apparently whatever they decide to do now becomes suspect, with the DM questioning if the action chosen is logical or metagamed. Even though it's probably both, and arguably even more of the former.

Quote from Llew_Llaw >>

 Have the fighter roll say a D20 (or whatever die the DM wishes) and that determines the direction he moves. That's what our DM got us to do when the characters were put into darkness.

 Could also have the fighter (or anyone) roll Perception (maybe a high DC) to notice where the spell exploded from (thus know where the center is).

Quote from Vince_Snetterton >>

Quote from kenclary >>

Quote from Llew_Llaw >>

 Have the fighter roll say a D20 (or whatever die the DM wishes) and that determines the direction he moves. That's what our DM got us to do when the characters were put into darkness.

 Could also have the fighter (or anyone) roll Perception (maybe a high DC) to notice where the spell exploded from (thus know where the center is).

 Contrary to revisionist history, and the parsing of the wording the spell, it is abundantly clear that Darkness falls simultaneously across the entire area. The Fighter has zero ability to figure out the epicenter. A ton of spells would be ruined if that was the case.

 ...or roll to see where the caster was pointing. Or guess where the optimal place to put a darkness spell would be. Or any other sane interpretation of "Magical darkness spreads from a point you choose" you want. (Well, as you stated, you don't want that interpretation, but you weren't the DM for the situation so it doesn't matter.)

Edit: you could also tell by sound. A Darkness spell makes a "light, light, go away, come again some other day" sound, while Blindness makes a "oh god, my eyes!" sound ;)

You could also have them make an Wis check to see if they're wise enough to guess it's a spell. And an Int check to be smart enough to run from the center. Or just assume, like I think the DM did, that all these adventurers have enough in-character common sense from living in a world of magic and dungeons and dragons to not have to play dumb about getting hit with a spell effect...