PDA

View Full Version : Running around a corner to sneak attack



ffone
2010-12-29, 12:13 PM
I'm trying to understand how to adjucate sneak attacks when you hide from an enemy b/c walls, etc. give you (total) cover but the square you're in doesn't 'intrinsically' provide concealment from all angles (like dense foliage).

Suppose you run around a corner, out of sight from everyone, but otherwise you're in a bare hallway (so you have total cover from everyone else at the moment, but otherwise there's nothing 'in' the hall providing cover or concealment).

Can you then make a Hide check? If someone follows after you, would a successful Hide vs their Spot mean that, even once they go around the corner, they don't 'see' you - they don't know what square you're in, and-or they are denied their Dex bonus if you attack (i..e you can sneak attack)?

Let's say the guy following you ends his turn at the corner (so he can see along both halls). Your rogue, on his turn, is more than 5' away....on your turn, can he move towards the other guy and sneak attack him? Would this require a second hide check (to maintain hidden-ness during that movement)?

(In this scenario everyone has acted at least once in combat and is not flat-footed).

Also, could the rogue make multiple attacks w/ sneak attack damage, or does the first attack un-Hide you?

Currently I have some enemies who will try to use tactics like this; I suspect any players targeted will object ("it's a bare hall! how could I not see the rogue the instant I came around the corner! I saw him go that way and was chasing him!") and am hoping to be able to either defend the tactic (citing SRD/DMG ideally) - or know ahead of time that I am wrong so I don't attempt it.

A related (perhaps equivalent) question - if you use cover to invoke the Hide skill, and then a creature moves to a position relative to which you no longer have cover (such as around a corner you went around) - does that automatically un-Hide you from them? Or do they still need to make a (passive/secret) spot check?

Eloel
2010-12-29, 12:17 PM
If they're not already in the battle, Surprise Round, the natural high initiative of sneak attacking (Dex-based) characters, and flatfooted enemies are what you're looking for.

Other than that, dunno.

Edit: Though one of the most important rules for Hide is that they need cover or concealment for it.

So, if the answer to "Do they have cover or concealment?" is "No", they can be (unless a specific ability says otherwise) seen.

ffone
2010-12-29, 12:26 PM
If they're not already in the battle, Surprise Round, the natural high initiative of sneak attacking (Dex-based) characters, and flatfooted enemies are what you're looking for.

Other than that, dunno.

That I know. I'm asking about a scenario after combat has started (everyone has acted) and a rogue runs off to 're-ambush'.



Edit: Though one of the most important rules for Hide is that they need cover or concealment for it.

So, if the answer to "Do they have cover or concealment?" is "No", they can be (unless a specific ability says otherwise) seen.

I'm asking about the 'timing' of that rule: if you have cover (and are momentarily 'unobserved', such as by total cover from being far enough around a corner) and hide, and then someone moves to a position from which you no longer have cover, does it un-Hide you (relative to them)? In order words, do you just need cover (and being unobserved) at the moment you make the hide check, or do you also need to have cover at the moment of the sneak attack?

If so, would it make a difference if, say, the rogue around the corner readies an action to make a (ranged) attack as soon as someone follows him around the corner?

ericgrau
2010-12-29, 12:35 PM
To hide you need cover (any physical obstacle) or concealment (any visual obstacle). You cannot hide against someone who has already seen you until you go out of sight again. Yeah total cover could do that. Technically, by RAW, you could even use the corner for cover (not total cover anymore) as you peek out again and make your sneak attack. Before they even run around it. After they run around it... well first you wouldn't see eachother at all, then a moment later you'd have (partial, not total) cover and would need to roll hide then a moment after that you'd have no cover and would be seen no matter how high your roll. Ya you could roll hide and ready-action sneak attack during that moment when you have (partial) cover.

Though as a DM I'd house rule in the Law of Paintball wherein you never poke your head out of the same spot twice (or the same corner you were just running around) or you will be seen.

Gamer Girl
2010-12-29, 08:37 PM
Suppose you run around a corner, out of sight from everyone, but otherwise you're in a bare hallway (so you have total cover from everyone else at the moment, but otherwise there's nothing 'in' the hall providing cover or concealment).

I know some people read in the rules that you can hide anywhere....I keep it simple in that you have to hide somewhere, behind something or such. You can not hide in a bare hallway.


Can you then make a Hide check? If someone follows after you, would a successful Hide vs their Spot mean that, even once they go around the corner, they don't 'see' you - they don't know what square you're in, and-or they are denied their Dex bonus if you attack (i..e you can sneak attack)?


You can't hide unless you have something to hide with, under, behind or such. You can not hide in an empty hallway



Let's say the guy following you ends his turn at the corner (so he can see along both halls). Your rogue, on his turn, is more than 5' away....on your turn, can he move towards the other guy and sneak attack him? Would this require a second hide check (to maintain hidden-ness during that movement)?

No, as the rouge would not be hidden in the empty hallway. And if the rouge was hidden behind a statue or such, they would be visible when they moved.


Also, could the rogue make multiple attacks w/ sneak attack damage, or does the first attack un-Hide you?

This depends. A rogue can make multiple sneak attacks vs a target that is still vulnerable to sneak attacks. For example, if a target is flat footed is flat footed until the take their first action..then they are flat footed for all the rouge's sneak attacks



Currently I have some enemies who will try to use tactics like this; I suspect any players targeted will object ("it's a bare hall! how could I not see the rogue the instant I came around the corner! I saw him go that way and was chasing him!") and am hoping to be able to either defend the tactic (citing SRD/DMG ideally) - or know ahead of time that I am wrong so I don't attempt it

You can simply have the enemy hide behind something. It's a movie classic...they run after the bad guy into the ball room..and see just tables and food and curtains..the bad guy could be hiding anywhere.

So don't have your dungeon so bare walled. Add rubble, statues, alcoves, pits, murder holes, secret doors, furniture, decorations and such. Even things like dead bodies work....'you run around the corner and see nothing but the giant lizard corpse.'

Also don't forget shadows, darkness, smoke, fog and so forth. You can hide in all of these.

This is what invisibility was invented for, naturally. Give them a couple potions of invisibility, or anything that makes darkness, smoke, fog or the like.



A related (perhaps equivalent) question - if you use cover to invoke the Hide skill, and then a creature moves to a position relative to which you no longer have cover (such as around a corner you went around) - does that automatically un-Hide you from them? Or do they still need to make a (passive/secret) spot check?

They have to be looking for you to make a spot check, or at least be aware your nearby and they have a chance to see you. You can make a spot check to see someone around a corner, anymore then you can see them inside a house.

ffone
2010-12-29, 09:42 PM
This depends. A rogue can make multiple sneak attacks vs a target that is still vulnerable to sneak attacks. For example, if a target is flat footed is flat footed until the take their first action..then they are flat footed for all the rouge's sneak attacks.

I'm not asking about flat-footedness (note that being denied a Dex bonus is not the same as flat-footed), but about the case where combat has already gone for a few rounds (everyone has acted and is not flat-footed) but the rogue hides and then full attacks.

Let's take a more traditional case - dense foliage providing concealment, so the rogue can hide in any square (as long as he's not presently observed.) He does so successfully, and luckily for him the enemy ends a turn adjacent to (but still unaware of) him. The rogue full attacks the enemy. Is every attack a sneak attack, or just the first?

awa
2010-12-29, 09:48 PM
their are rules in one of the books i forget which that lets you move out of cover and stay hidden the dc jump a lot and think it only works during your turn but if you were good enough or the enemy was bad enough you you move from one patch of cover to another or slip up behind a foe to stab them. Alas i only know its in the rules compendium.

ericgrau
2010-12-29, 09:51 PM
I'm not asking about flat-footedness (note that being denied a Dex bonus is not the same as flat-footed), but about the case where combat has already gone for a few rounds (everyone has acted and is not flat-footed) but the rogue hides and then full attacks.

Let's take a more traditional case - dense foliage providing concealment, so the rogue can hide in any square (as long as he's not presently observed.) He does so successfully, and luckily for him the enemy ends a turn adjacent to (but still unaware of) him. The rogue full attacks the enemy. Is every attack a sneak attack, or just the first?

Just the first because he is revealed after that. Even if he could stay hidden there's a -20 penalty, and typically hiding must be done as part of a move. The FAQ allows this if you have both spring attack (to move back to concealment, even if it is in the same square as you I think) and hide in plain sight, the ability that lets you hide again even after you've been observed.

Grendus
2010-12-29, 10:17 PM
I'd say (and this is total dm fiat, it just makes sense to me) that the rogue could hide behind the corner, but could only gain sneak attack if he readied an action to strike the first creature that came around the corner. He would still have to make an opposed hide check to hide around the corner without being seen, but the corner would provide cover and concealment until just after his opponent came within reach.

Makes for a great ambush, and a fun tactic. But that's just me.

WarKitty
2010-12-29, 10:22 PM
I'm not asking about flat-footedness (note that being denied a Dex bonus is not the same as flat-footed), but about the case where combat has already gone for a few rounds (everyone has acted and is not flat-footed) but the rogue hides and then full attacks.

I'd have to find them, but there are rules about mid-battle surprise rounds and flat-footedness, when someone is unaware of one of the attacking parties.

Personally, I'd go with Grendus - the rogue can make a sneak attack if he has a readied action to hit the first enemy that goes around the corner. He's hitting them before they've had a chance to look around.

Curmudgeon
2010-12-30, 12:25 AM
There have been a bunch of errors, house rules, and opinions expressed here. The following answers include none of those; it's all straight from the RAW.

Suppose you run around a corner, out of sight from everyone, but otherwise you're in a bare hallway (so you have total cover from everyone else at the moment, but otherwise there's nothing 'in' the hall providing cover or concealment).

Can you then make a Hide check?
No. Hide is an opposed check. Total concealment means there's no line of sight to anyone who could make the necessary opposed Spot check.

If someone follows after you, would a successful Hide vs their Spot mean that, even once they go around the corner, they don't 'see' you - they don't know what square you're in, and-or they are denied their Dex bonus if you attack (i..e you can sneak attack)?
That can't happen, because you have no way to Hide (no cover/concealment) once they gain line of sight to your position.

Let's say the guy following you ends his turn at the corner (so he can see along both halls). Your rogue, on his turn, is more than 5' away....on your turn, can he move towards the other guy and sneak attack him? Would this require a second hide check (to maintain hidden-ness during that movement)?

(In this scenario everyone has acted at least once in combat and is not flat-footed).
Again, for the reason noted above, this can't happen.

Let me revise the scenario into something that could happen.

Let's say you (the Rogue) go around the corner into the empty hall (breaking line of sight to everyone, thus establishing the "not being observed" condition), then turn again to be just around another corner, gaining partial cover from people following into the hall. Immediately, you can make no Hide check because there's no one who could Spot you. But when someone follows into that empty hall, you do get to Hide: you're not being observed, and you've got cover.

Using the Move between Cover rules (Complete Adventurer, pages 101-102) you would have a chance to sneak up on the follower and (if successful) sneak attack them.

Also, could the rogue make multiple attacks w/ sneak attack damage, or does the first attack un-Hide you? You can make a sneak attack whenever you've established the requirements (flanking, or target denied their DEX bonus to AC). If you're trying to deny the opponent's DEX bonus by being visually undetectable, you would need to have made a successful Hide check for any attack. Usually that's not possible after the first swing when you attack from hiding: you're noticed when you make that first attack, plus can't use Move between Cover again unless you move again, so you fail on both Hide requirements.

The Hide in Plain Sight special ability is the most common way to overcome the "not being observed" requirement. Most versions of HiPS (the Extraordinary ones, mainly) don't do anything about the cover/concealment requirement, so you'd need some way to solve that problem as well. (Rangers, for instance, solve this with their separate Camouflage class feature.)

A related (perhaps equivalent) question - if you use cover to invoke the Hide skill, and then a creature moves to a position relative to which you no longer have cover (such as around a corner you went around) - does that automatically un-Hide you from them? Or do they still need to make a (passive/secret) spot check?
You only make Hide checks when there's an opposed Spotter, so staying hidden means making a successful Hide check every time someone gets to make a Spot check to see you.
Every time you have a chance to spot something in a reactive manner you can make a Spot check without using an action. When they move into a position where there's no longer cover between you and them, that's something different for them to react to: they get a free Spot check. At that time you're not allowed to Hide (no cover) but you might still go undetected if your potential observer's lack of skill makes it difficult for them to see you.
The Spot skill is used primarily to detect characters or creatures who are hiding. Typically, your Spot check is opposed by the Hide check of the creature trying not to be seen. Sometimes a creature isnít intentionally hiding but is still difficult to see, so a successful Spot check is necessary to notice it. From Table 4Ė3: Difficulty Class Examples (Player's Handbook, page 64):
{table=head]Difficulty (DC)|Example (Skill Used)
Very easy (0) | Notice something large in plain sight (Spot)[/table]
If you're Medium size and 30' away the effective DC to Spot you is 7: +4 for being 1 size step below Large, +3 for each 10' of distance. (OK, the actual mechanism specified is they reduce their roll by 1 for each 10' of distance. Boosting the DC instead is mathematically identical.)

While an observer's poor Spot skill might leave them unaware of you, that by itself doesn't let you sneak attack them; it only makes you visually undetected. You need to be visually undetectable to deny them their DEX bonus to AC, and without cover/concealment you can't get that.

JackMage666
2010-12-30, 01:23 AM
This sounds like one of those situations where RAW doesn't quite cover what's intended. I imagine what this Rogue is trying to do is feign fleeing. When someone comes around the corner, the Rogue has hidden in the blind spot, and plans to strike the attacker before he fully realizes the situation.

Were I the DM, I'd plan it something like this -

1. Rogue uses move action to flee around the corner.

2. A. I'd probably ask him to make a hide check (fairly low DC, as he's ducking back against the wall, out of sight. However, if he botched the check, maybe he overestimated how much room he had and his foot is sticking out and into sight, thus ruining the surprise.

2. B. Since it's a unique situation, I'd probably like the Rogue to make a bluff check to convince the people he's fleeing. They'd make an opposed Sense Motive check (unmodified by BAB, unlike a normal feint.) If they failed the Sense Motive check, they think he ran.

3. Rogue readies an action to strike anything that comes around the corner. He'll get one attack that treats the foe as flat footed.

Anyone that moves behind the corner is subject to that attack. Which sucks if one of his allies isn't aware of his plan and decides to join him in fleeing. Maybe I'd allow a reflex save to stop not attack an ally.

The point is, RAW, this likely isn't going to happen too easily. But, I think if the players are being clever, the rules can be manipulated to make it work.

ffone
2010-12-30, 02:27 AM
Thanks for your answers, Curmudgeon. One thing:



No. Hide is an opposed check. Total concealment means there's no line of sight to anyone who could make the necessary opposed Spot check.




Let's say you (the Rogue) go around the corner into the empty hall (breaking line of sight to everyone, thus establishing the "not being observed" condition), then turn again to be just around another corner, gaining partial cover from people following into the hall. Immediately, you can make no Hide check because there's no one who could Spot you. But when someone follows into that empty hall, you do get to Hide: you're not being observed, and you've got cover.

So, indeed, total cover (going around the corner, possibly several squares past the turn depending on the angles of others near it) obviates the need for a Hide check at all....but since the rogue might find themselves with only partial cover once someone else begins moving toward them, presumably a Hide check is called for at that point.

But a Hide check is part of the rogue's turn (made while he moves). The subtlety is that total/partial/no cover is not an absolute state of a character, but rather a relative state between one character and another, which can be changed by the movements of others...whereas a Hide check is (generally) made as part of a rogue's movement.

So even though the rogue has total cover when he moves - wouldn't you make the Hide roll at that point? Or would you wait until it becomes relevant b/c someone chases far enough to reduce it to partial cover?



Using the Move between Cover rules (Complete Adventurer, pages 101-102) you would have a chance to sneak up on the follower and (if successful) sneak attack them.

Awesome, thanks. I had previously been figuring what the last few posters said: you'd probably need to ready an action to attack - unless you get lucky and the follower ends his movement in the square where you have partial but not total cover, so you can sneak attack him.

The move between cover rule appears to add a little flexibility: for example, if the follower ends his movement a few squares shy of where you'd normally ambush him - in a spot from which he still has total cover from you, and/or you couldn't reach him w/o breaking your own cover - you might be able to move back around the corner and attack once and still deny his Dex bonus.

In this 'bare hallway corner' scenario readying an action is probably still the typically advisable tactic. But you could make up a scenario where not readying an action is preferable (you're confident the other guy will run out of movement a few squares shy of the corner, and you have a swift move + full attack ability, so you'd rather not ready an action, which has to be only a standard action. Even if your iteratives won't be sneak attacks.)

SilverLeaf167
2010-12-30, 03:54 AM
Regarding the same matter (sort of): if I ran around a corner and then made a Climb check to get up into the ceiling, Hiding there, would I be able to make a Sneak Attack by falling on the opponent before they have seen me? You know, like this (http://www.youtube.com/watch?v=dLvdxvmcWQo)?

Yora
2010-12-30, 04:47 AM
I think this is one of the cases in which the rules as they are written say no, but it is very easy for a gm to make it possible anyway without much trouble.
I'd say a case like this is highly situational and very hard to make a hard rule for. But if the action seems plausible and it makes the game more exiting for everyone, a good gm should come up with a house rule or even decide to break the written rules on the spot. D&D 3.5e is one of the few games in which the books don't explicitly say one should adjust the rules to the needs of the group. Most other systems I've read about do have such a note right at the beginning of the primary rule book.

In this case, I would say that running behind a corner and ready an action to stab at the very first thing that comes around that corner seems well within the ability of a rogue and seems to be a plausible action.
You could have both characters make an initiative check to determine if the rogue can stab the other character before he is completely aware of him. If the rogue wins, his attack is a sneak attack. If the other character wins initiative, it's a regular attack that does not deal SA damage.

Running out of cover and sneaking up to a character that is already aware that a fight is going on is more complicated. RAW says all characters have all around vision once a fight has started. Sneaking up to a character in melee seems so dificult, that I simply wouldn't allow it at all.
Sneaking up on an archer or a spellcaster who is shoting and casting spells from the edge of the battlefield is a completely different thing, however. But I would say that a rogue could make both a hide and move silently check to sneak up to such a target and make a Sneak Attack if the target doesn't notice him. Maybe give the target a +4 bonus to his checks, because he should be paying some attention to what's going on next to him. But when the rogue readies an action to come out of cover right when the character starts to aim an arrow or cast a spell, it would seem appropriate that the target is focusing all his attention on something else than his back.
The gm should judge if such a situation is given case by case. It does not seem like a good idea to come up with a hard rule when such things are possible and when not.

Curmudgeon
2010-12-30, 04:55 AM
But a Hide check is part of the rogue's turn (made while he moves). The subtlety is that total/partial/no cover is not an absolute state of a character, but rather a relative state between one character and another, which can be changed by the movements of others...whereas a Hide check is (generally) made as part of a rogue's movement.

So even though the rogue has total cover when he moves - wouldn't you make the Hide roll at that point? Or would you wait until it becomes relevant b/c someone chases far enough to reduce it to partial cover?
This is one place where the turn-based D&D mechanics fit oddly when attempting to model simultaneous actions. However, as a Hide check is not an action in itself, you can make it on someone else's turn just as you can make a saving throw; that's the nature of opposed rolls.

A character can't Hide until another character has a line of sight for their opposed Spot check, but they're supposedly piggy-backing that Hide check on an action that's already been completed (in this same turn). In a similar exposition of the awkwardness of this mechanic, the conditions for that Hide check aren't known until the opponent arrives (possibly bringing an illumination source and changing the available concealment situation). So you're basically left with the following intersection of the various rules:

You (try to) Hide at the end of your turn, even if you don't see any potential observers. (This would be the right approach if any potential Spotters were invisible, for instance.)
You don't actually use any Hide rolls until later when the DM requires them to oppose an (unknown perhaps) enemy's Spot.

Psyx
2010-12-30, 08:54 AM
/scroll.

/throw rulebook away.


Let's say we're fighting. You run off around a corner and press yourself against a wall, in plain view, but around the corner.

I run around the corner after you.

Am I going to be surprised to find you standing right around the corner with a knife in your hand?

Obviously not, unless I'm depressingly stupid. So: No sneak attack bonus.

Fable Wright
2010-12-30, 09:01 AM
/scroll.

/throw rulebook away.


Let's say we're fighting. You run off around a corner and press yourself against a wall, in plain view, but around the corner.

I run around the corner after you.

Am I going to be surprised to find you standing right around the corner with a knife in your hand?

Obviously not, unless I'm depressingly stupid. So: No sneak attack bonus.
Perhaps not in plain sight, though. Unless your body is incredibly thick, if you hide behind a wall the right way, you can't really be seen. Until the other person runs around the corner, they don't know whether you have kept running or hid behind the corner. Coupled with the surprise of being lunged at from the shadows (which is always shocking), the person chasing out is probably shocked enough for you to get off a sneak attack.

WarKitty
2010-12-30, 09:18 AM
/scroll.

/throw rulebook away.


Let's say we're fighting. You run off around a corner and press yourself against a wall, in plain view, but around the corner.

I run around the corner after you.

Am I going to be surprised to find you standing right around the corner with a knife in your hand?

Obviously not, unless I'm depressingly stupid. So: No sneak attack bonus.

So require a stealth or bluff check or something. If you're in the middle of a battle, I wouldn't guarantee that you noticed. Or if I acted like I was running away from the battle.

Psyx
2010-12-30, 09:31 AM
if you hide behind a wall the right way, you can't really be seen. Until the other person runs around the corner, they don't know whether you have kept running or hid behind the corner. Coupled with the surprise of being lunged at from the shadows (which is always shocking), the person chasing out is probably shocked enough for you to get off a sneak attack.

Did nobody here play tag or similar* at school?

If someone 'runs away' around a corner, you'd have to be blisteringly-failed-a-sense-motive-check-at-plus-fifty-stupid to run around the corner after them, because 90% of the time they are going to be standing right around the corner, waiting for you. I'd say that this was the oldest trick in the book, but I'm not sure if I was old enough to be reading books by the time that I'd figured this one out...

You run OUT from the corner before rounding it, so you come at it wide and comfortably out of reach. Just in case someone is standing just around it to punch you...err... I mean 'tag' you. So if they have run away, you've lost about 5-10 feet on them, and if they haven't they are standing there with no element of surprise.
If you can't run wide because it's a passage, then you step carefully: Either they're actually running away, in which case they're out of the fight and it doesn't matter if you loose them, or they're standing there now going 'erm' and you get to 'tag' them/kick them in the goolies.

Why on earth would one forget this lesson when given 4 foot of steel to murder the other person with, in the sure knowledge that the other person has a equally sharp piece of metal for the same reason.

Extra bonus points for stupidity if the guy you are chasing is carrying daggers and wearing light armour... because obviously they'd never be likely to be standing around a corner waiting for you, would they? :smallconfused:



*like the old childhood favourite: Chase someone, catch them, and give them a beating.

Vistella
2010-12-30, 09:43 AM
just hide behind your towershield, then youre invisible :smallbiggrin:

Psyx
2010-12-30, 09:56 AM
Why not give the guy chasing the guy around the corner a sneak attack as he rounds the corner suddenly? After all, he has total cover from the person he's chasing... The guy waiting around the corner might be completely surprised by the fact.

This sounds like an absurdity. It is. But it serves as an illustration.

The person being chased is about as likely to be surprised by the person running around the corner as the other way around. ie: Not very, unless they have the memory of a goldfish. They know the foe is there somewhere, and they have a good reason to believe that they might be right around the corner.

WarKitty
2010-12-30, 09:59 AM
Why not give the guy chasing the guy around the corner a sneak attack as he rounds the corner suddenly? After all, he has total cover from the person he's chasing... The guy waiting around the corner might be completely surprised by the fact.

This sounds like an absurdity. It is. But it serves as an illustration.

The person being chased is about as likely to be surprised by the person running around the corner as the other way around. ie: Not very, unless they have the memory of a goldfish. They know the foe is there somewhere, and they have a good reason to believe that they might be right around the corner.

I can think of plenty of situations where the person wouldn't know that they're there. A successful bluff check would probably be the easiest. And that's why I said they'd need a readied action, so as to get the person before they had a chance to look around.

ffone
2010-12-30, 03:15 PM
/scroll.

/throw rulebook away.


Let's say we're fighting. You run off around a corner and press yourself against a wall, in plain view, but around the corner.

I run around the corner after you.

Am I going to be surprised to find you standing right around the corner with a knife in your hand?

Obviously not, unless I'm depressingly stupid. So: No sneak attack bonus.

By this same logic, Blindsense defeats sneak attack, as does successful Listen vs an invisible guy.

Sneak attack doesn't require the guy have no idea you exist or are in that square. A character may know they are about to get sneak attacked and from where...and it can still be a sneak attack - even though a lay person who didn't know what Sneak Attack means in DnD might not call it a 'sneak attack'.

(The reason you are wrong is b/c, as you said yourself, you're 'throwing the rulebook' away and using the lay English meaning of 'sneak attack' - but game concepts are not defined by their everyday meanings. See for example every argument thread about ability scores.)

My in-character interpretation is that, if he can't see you directly, he doesn't know the precise timing/angle of your dagger-thrust or whatever, and can't effectively defend himself.