1. Perception check for the townsfolk close enough to notice the arriving combatants.
2. Insight check for those that pass perception to determine whether they realize that there's a fight.
3. Any townsfolk who fail both checks are surprised until the end of the round in which they noticed the fight.
Townsfolk are all going to have similar stats because they are level 0, so I'd just roll percentile dice twice then take the lower roll to approximate how many people are surprised and who aren't...especially if there are more than 2 or 3 townsfolk that get caught in the middle.
I haven't read the previous comments or looked at RAW before writing this answer, but my impression of the Surprise rules is that the mechanic is only used at the start of combat, i.e. when you go from no combat to combat. I'd say that it makes sense not to grant Surprise again if a new enemy shows up during combat, as your adrenaline is probably already way up at that point (which is also why it makes sense to grant Surprise at the beginning of combat when your level of adrenaline goes from low to high).
Basically, yeah. The surprise mechanic is only for the purpose of initiating a combat encounter from a state in which no combat was already occurring, for the parties which become actively involved. Here's the excerpt on surprise from the basic rules:
Surprise
A band of adventurers sneaks up on a bandit camp, springing from the trees to attack them. A gelatinous cube glides down a dungeon passage, unnoticed by the adventurers until the cube engulfs one of them. In these situations, one side of the battle gains surprise over the other.
The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn't notice a threat is surprised at the start of the encounter.
If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends. A member of a group can be surprised even if the other members aren't.
If a battle spills over to an area where another group of NPCs is located, the default is just the normal sequence for combat. If the "new" group are trying to join combat stealthily, that resolves as normal for a hidden creature in combat. If the new group of NPCs are just "there", then there's no real surprise. They join the initiative order, and act as normal.
The underlying implication of a "surprise round" is that hostile actions are actually taken against the surprised party. You are "surprised" because there's suddenly a knife in your back, the buddy you're walking home with suddenly bursts into flames, your camp is suddenly showered with arrows, etc.
In the example of dueling casters teleporting into a town, are those casters attacking townsfolk immediately upon appearing in town, or are they still just fighting each other? Do they teleport in simultaneously? If one caster teleports out and immediately starts attacking townsfolk, then effectively a brand new combat encounter has begun and I would check for surprise, but that still only applies if the attacking party is actually trying to stealthily initiate combat. Popping out of a Dimension Door in the town square is a very visible thing, but you could still surprise someone by going through invisibly and attacking.
If both casters teleport in and just continue attacking each other, without directly having an effect on town NPCs, then the previous combat encounter has just shifted to a new location. It would be very surprising for their new audience, but (mechanically) they are not surprised.
You don't know what fear is until you've witnessed a drunk bird divebombing you while carrying a screaming Kobold throwing fire anywhere and everywhere.
Eh, you could tweak the encounter to gain the same effect. The hypothetical was just that, a scenario to highlight the unknown variable in the rules interaction. So maybe I should simply stick to the question directly if people are stuck on just that one example...
Two sides are already locked in ongoing combat. This battle spills onto a 3rd group who are surprised by the combatants. They did not expect this combat and were simply going about their business. One or both of the initial combatants have the potential to attack or otherwise harm the 3rd surprised group, or the 3rd group might have cause to be hostile to one or both of the ongoing combat participants. How is this resolved, mechanically, in the most RAW way possible? Does this situation simply require making up your own rules?
The simplest explanation would be that there is no surprise for the 3rd group. Combat is already happening. As the combat draws nearer to the 3rd group, it will be noticed.
In "the most RAW way possible", if you as the DM believe it's even possible for the 3rd group to not notice a proverbial angry horde next door (blind, deaf, lacking any nerve endings to sense vibrations, etc.), then the process is still the same as always: stealth checks vs. passive perceptions.
In such a situation, I would use the passive stealth of the groups already in combat, and I would start doing those checks well before the battle actually lands on the 3rd group. There's a table somewhere that has modifiers based on distance (applicable to stealth, perception, or both), so the closer the battle gets to the 3rd group, the more likely it is they'll actually notice what's going on.
If we're just talking about town NPCs, then you as the DM get to decide how they behave. An NPC that notices the combat might alert everyone around them, or they might just bolt. Either way, insert them into your initiative order, so you can start determining how they react. If an NPC somehow manages to not notice anything by the time the battle actually reaches them, yeah they're totally oblivious.
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You don't know what fear is until you've witnessed a drunk bird divebombing you while carrying a screaming Kobold throwing fire anywhere and everywhere.
The simplest explanation would be that there is no surprise for the 3rd group. Combat is already happening. As the combat draws nearer to the 3rd group, it will be noticed.
I disagree with this. Mainly if the 3rd party had no awareness of a combat occurring because the combat was occurring a healthy distance away from them, they'd be new entrants when the Wizard's bamf in. As such, you'd go back to step 1 in the checklist and determine surprise for those new entrants, determine positioning, and roll initiative for them. The Wizards wouldn't be surprised because they were already actively in combat.
That said, this issue is completely a RAI one, since there is nothing stating to start back at step 1 for new entrants of any sort, but it is the most logical conclusion to come to for things that were minding their own business when suddenly they get caught between two people fighting.
In your specific example, are the townsfolk participants in the battle? Do they attack or get attacked? Or are they just bystanders?
Bystanders don't get a turn in the initiative. If two batting wizards teleport into the middle of a town, give them 1d4 rounds until the guards show up and add them to the initiative.
RAW: A third party can be surprised by the sudden appearance of two warring parties, but it is unlikely because according to the rules, both warring parties would have to be trying to sneak (which would be unusual).
Townsfolk are all going to have similar stats because they are level 0, so I'd just roll percentile dice twice then take the lower roll to approximate how many people are surprised and who aren't...especially if there are more than 2 or 3 townsfolk that get caught in the middle.
Good call on the percentile; far more efficient than what I was thinking!
Echoing your notion of going back to step 1, the segment of RAW I would turn to when attempting to make such a ruling is this: "Any character or monster that doesn't notice a threat is surprised at the start of the encounter."
I'd ignore whether it's the start of the encounter as a whole and instead consider whether it's the start of the encounter for any specific creature. If it's unaware of the fight at that moment, then I'd rule it's surprised.
By that logic: when the townspeople are added to initiative, it's the start of the encounter for them, and therefore they can be surprised. Does that seem sensible?
Townsfolk are all going to have similar stats because they are level 0, so I'd just roll percentile dice twice then take the lower roll to approximate how many people are surprised and who aren't...especially if there are more than 2 or 3 townsfolk that get caught in the middle.
Good call on the percentile; far more efficient than what I was thinking!
Echoing your notion of going back to step 1, the segment of RAW I would turn to when attempting to make such a ruling is this: "Any character or monster that doesn't notice a threat is surprised at the start of the encounter."
I'd ignore whether it's the start of the encounter as a whole and instead consider whether it's the start of the encounter for any specific creature. If it's unaware of the fight at that moment, then I'd rule it's surprised.
By that logic: when the townspeople are added to initiative, it's the start of the encounter for them, and therefore they can be surprised. Does that seem sensible?
That's how I'd run it, as it is effectively the start of the encounter for them as you noted.
EDIT: Just to point out, this wouldn't be the case for things joining the encounter late since i'd roll their initiative as soon as combat starts and follow the normal sneaking rules if they are trying to do it stealthily to 'surprise' the opposing force.
E.g. if one of the wizards had a few allies ready to ambush the other as soon as they dimension door, then those guys who are waiting among the townsfolk would already be in initiative and would not be surprised?
Don't think there is a specific rule. I would have the townspeople in the square check for surprise and then roll an initiative score. The two wizards would carry on at their same initiative and would not be surprised.
Yeah that's my instinct as well but I've had people tell me I'm wrong and that that there simply cannot be any surprised parties after combat has started under any circumstance, and that the townsfolk in that example aren't surprised because combat is already ongoing, despite it being new to them.
I guess though you'd have to check for surprise mid-round, because that's when they get pulled into the combat. So if their initiative is higher than the event that pulled them into combat they're not surprised... and if they have a lower initiative they are surprised? Otherwise they'd be outside combat, while being in combat, until the round ended... which doesn't seem to work either.
If they are surprised and their initiative has already passed, they won't take a turn anyway until the next round.
E.g. if one of the wizards had a few allies ready to ambush the other as soon as they dimension door, then those guys who are waiting among the townsfolk would already be in initiative and would not be surprised?
Just so, that is closer to the Grick at Cragmaw Castle than the oblivious townsfolk. They might be momentarily startled that it happened, but they would have been expecting it and mechanically not been surprised (much like getting startled because of fireworks, a friend firing a gun, or something of the sort). They could have had readied actions for when the wizards teleported in that would trigger if their initiative precedes the wizards entry.
E.g. if one of the wizards had a few allies ready to ambush the other as soon as they dimension door, then those guys who are waiting among the townsfolk would already be in initiative and would not be surprised?
That is exactly what I would do, yes. They were prepared for the fight, even if they weren't prepared for the fight to come to them so to speak. As such I'd have rolled initiative for them already (or if they were PC's I'd have them roll)
I agree with those who say the townsfolk would not be surprised in the game mechanics sense but, surprised in the literal sense. The Surprise mechanic seems to indicate that the intent of at least one creature from a group of opposing forces wishes to take an action while undetected. Further, the rules state that beings not actively trying to stay undetected through some means, automatically detect each other. If that settles that particular question for you, I'd like to pose another, more commonly occuring conundrum.
Let's say Group A is approaching Group B. Group A is aware of Group B, Group B is NOT aware of Group A. Most of Group A is not hiding their presence and will be detected by Group B. Group A has a Rogue that all of Group B fails to detect. Group B is Surprised even though they are aware of all of Group A's other members.
I have a few ideas to moderate this situation but, it would be some heavy house rules. I'd like to see what others come up with before i post my "solution".
1) Group B is surprised by the Rogue from Group A only if the Rogue is approaching from an unexpected direction, like the ceiling, the floor, or from behind total cover. Otherwise, why would Group B not anticipate a creature (the Rogue) approaching when they know that Group A is approaching?
2) If combat is initiated only by the Rogue, Group B cannot respond to the Rogue's initial action+bonus action if #1 is true. So long as the rest of Group A is not intending for this to be a hostile interaction and are not aware of the Rogue's aggressive intention, they too are surprised. If they knew of the Rogue's intent to attack but oppose that line of action, they would not be surprised and can act as normal, perhaps shouting a warning to Group B and thereby preventing Group B from being surprised at all.
3) However, if combat is initiated by all or most of Group A against Group B, then I would say that Group B is not surprised. So then everybody rolls initiative, with the Rogue getting a bonus of +3 to +6 depending on the circumstances of their stealthy approach.
And you've just highlighted how I feel surprise rules fail without a surprise round before normal initiative/combat.
For 1, you tell me. This is going to be the most common scenario for a class to deal with that relies on Stealth. For the sake of semantics, if the rest of group a is terrible at Stealth and will fail, it's mechanically the same as not trying to Stealth.
For 2, if the party is in full agreement, they let the Rogue start the engagement by taking ready action and using reaction to do what they plan to do. This however, pretty much contradicts another SA ruling on delaying your turn. If the group is not aware of the Rogue's intent or not in agreement, the Rogue becomes Group C. Then it also becomes a matter of who encounters who first.
For 3, I totally agree.
Now for a second round of mechanical issues. I'm going to use a more simple example. Group A consists of two Rogue thieves called 1 and 2. Group B is a lone passerby. Both Rogues roll Stealth, 1 fails against passive detection by B and 2 succeeds. Initiative finds 1 going first, then B, lastly 2. Yet again SA complicates the situation by saying that "you can be surprised even if your companion aren't, you aren't surprised if even one of your foes fails to catch you unawares."
Adding numerous conditions makes a successful Surprise attack less and less likely. The quoted line means that if even one of you allies fails to Surprise a targets, so do you.
... Yet again SA complicates the situation by saying that "you can be surprised even if your companion aren't, you aren't surprised if even one of your foes fails to catch you unawares."
Adding numerous conditions makes a successful Surprise attack less and less likely. The quoted line means that if even one of you allies fails to Surprise a targets, so do you.
Yes. It is difficult. Because the consequences of being surprised can be catastrophic. Remember that there is a major difference between being Surprised and just not being able to see one or more of your attackers. Surprise means you are caught off-guard, hands away from weapons, defenses down, distracted. So unawares that you can't do anything useful at all - and you are open to an Assassin's devestating auto-crit sneak attack.
In your example of two thieves attacking and one failing the stealth check - well that failure was the cracking twig that literally ruins the surprise attack for both. No surprise for anyone.
That being said, there are still very many benefits to an ambush even without achieving surprise. The hidden Rogue may not surprise the enemy, but it is still hidden; untargetable until discovered and almost guaranteed advantage and sneak damage on first attack. Ambushers tend to have better cover. The DM might see fit to grant advantage on initiative rolls to a group launching such an attack, and so on and so forth.
If you only had 1 attack per turn and could rarely use the defining feature of your subclass as Rogue /Assasin , that would be pretty annoying. There has to be a better mechanical middle ground for the Surprise scenario. I don't even have a Stealth dog in the fight. I'm the Cleric stomping around in heavy armor with no Stealth, dex or anything remotely resembling a quiet approach.
Surprise in 5e is much more specific and less common than previous additions. At least that is my understanding.
For example, just because something unexpected happens, it doesn't mean you are "surprised" mechanically even if you might well be surprised by the turn of events.
Consider two groups where some members of one group are hidden. These members do not get a "surprise" round. No one is surprised since they have possibly hostile opponents and they are aware that something may be happening. Just because some folks aren't noticed doesn't give them mechanical surprise (though they would have advantage on their attacks if the DM rules that they are hidden ... eg a rogue passing a stealth check before combat starts). However, if ANY of the party are noticed then there is no surprise.
The only times I have found where surprise occurs is when one side is prepared for combat and jumps in against an opposing side that is unaware that combat is imminent. This has happened in games I have played where one side sets up a particularly well planned ambush and are not noticed before they start attacking. It also happened when the party jumped through a portal into a room with unprepared enemies.
Other than that, the DM has to rule whether surprise is applicable or not and in most cases it is not.
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Townsfolk are all going to have similar stats because they are level 0, so I'd just roll percentile dice twice then take the lower roll to approximate how many people are surprised and who aren't...especially if there are more than 2 or 3 townsfolk that get caught in the middle.
Basically, yeah. The surprise mechanic is only for the purpose of initiating a combat encounter from a state in which no combat was already occurring, for the parties which become actively involved. Here's the excerpt on surprise from the basic rules:
If a battle spills over to an area where another group of NPCs is located, the default is just the normal sequence for combat. If the "new" group are trying to join combat stealthily, that resolves as normal for a hidden creature in combat. If the new group of NPCs are just "there", then there's no real surprise. They join the initiative order, and act as normal.
The underlying implication of a "surprise round" is that hostile actions are actually taken against the surprised party. You are "surprised" because there's suddenly a knife in your back, the buddy you're walking home with suddenly bursts into flames, your camp is suddenly showered with arrows, etc.
In the example of dueling casters teleporting into a town, are those casters attacking townsfolk immediately upon appearing in town, or are they still just fighting each other? Do they teleport in simultaneously? If one caster teleports out and immediately starts attacking townsfolk, then effectively a brand new combat encounter has begun and I would check for surprise, but that still only applies if the attacking party is actually trying to stealthily initiate combat. Popping out of a Dimension Door in the town square is a very visible thing, but you could still surprise someone by going through invisibly and attacking.
If both casters teleport in and just continue attacking each other, without directly having an effect on town NPCs, then the previous combat encounter has just shifted to a new location. It would be very surprising for their new audience, but (mechanically) they are not surprised.
You don't know what fear is until you've witnessed a drunk bird divebombing you while carrying a screaming Kobold throwing fire anywhere and everywhere.
Eh, you could tweak the encounter to gain the same effect. The hypothetical was just that, a scenario to highlight the unknown variable in the rules interaction. So maybe I should simply stick to the question directly if people are stuck on just that one example...
Two sides are already locked in ongoing combat. This battle spills onto a 3rd group who are surprised by the combatants. They did not expect this combat and were simply going about their business. One or both of the initial combatants have the potential to attack or otherwise harm the 3rd surprised group, or the 3rd group might have cause to be hostile to one or both of the ongoing combat participants. How is this resolved, mechanically, in the most RAW way possible? Does this situation simply require making up your own rules?
I got quotes!
The simplest explanation would be that there is no surprise for the 3rd group. Combat is already happening. As the combat draws nearer to the 3rd group, it will be noticed.
In "the most RAW way possible", if you as the DM believe it's even possible for the 3rd group to not notice a proverbial angry horde next door (blind, deaf, lacking any nerve endings to sense vibrations, etc.), then the process is still the same as always: stealth checks vs. passive perceptions.
In such a situation, I would use the passive stealth of the groups already in combat, and I would start doing those checks well before the battle actually lands on the 3rd group. There's a table somewhere that has modifiers based on distance (applicable to stealth, perception, or both), so the closer the battle gets to the 3rd group, the more likely it is they'll actually notice what's going on.
If we're just talking about town NPCs, then you as the DM get to decide how they behave. An NPC that notices the combat might alert everyone around them, or they might just bolt. Either way, insert them into your initiative order, so you can start determining how they react. If an NPC somehow manages to not notice anything by the time the battle actually reaches them, yeah they're totally oblivious.
You don't know what fear is until you've witnessed a drunk bird divebombing you while carrying a screaming Kobold throwing fire anywhere and everywhere.
I disagree with this. Mainly if the 3rd party had no awareness of a combat occurring because the combat was occurring a healthy distance away from them, they'd be new entrants when the Wizard's bamf in. As such, you'd go back to step 1 in the checklist and determine surprise for those new entrants, determine positioning, and roll initiative for them. The Wizards wouldn't be surprised because they were already actively in combat.
That said, this issue is completely a RAI one, since there is nothing stating to start back at step 1 for new entrants of any sort, but it is the most logical conclusion to come to for things that were minding their own business when suddenly they get caught between two people fighting.
In your specific example, are the townsfolk participants in the battle? Do they attack or get attacked? Or are they just bystanders?
Bystanders don't get a turn in the initiative. If two batting wizards teleport into the middle of a town, give them 1d4 rounds until the guards show up and add them to the initiative.
RAW: A third party can be surprised by the sudden appearance of two warring parties, but it is unlikely because according to the rules, both warring parties would have to be trying to sneak (which would be unusual).
Good call on the percentile; far more efficient than what I was thinking!
Echoing your notion of going back to step 1, the segment of RAW I would turn to when attempting to make such a ruling is this: "Any character or monster that doesn't notice a threat is surprised at the start of the encounter."
I'd ignore whether it's the start of the encounter as a whole and instead consider whether it's the start of the encounter for any specific creature. If it's unaware of the fight at that moment, then I'd rule it's surprised.
By that logic: when the townspeople are added to initiative, it's the start of the encounter for them, and therefore they can be surprised. Does that seem sensible?
That's how I'd run it, as it is effectively the start of the encounter for them as you noted.
EDIT: Just to point out, this wouldn't be the case for things joining the encounter late since i'd roll their initiative as soon as combat starts and follow the normal sneaking rules if they are trying to do it stealthily to 'surprise' the opposing force.
E.g. if one of the wizards had a few allies ready to ambush the other as soon as they dimension door, then those guys who are waiting among the townsfolk would already be in initiative and would not be surprised?
If they are surprised and their initiative has already passed, they won't take a turn anyway until the next round.
Just so, that is closer to the Grick at Cragmaw Castle than the oblivious townsfolk. They might be momentarily startled that it happened, but they would have been expecting it and mechanically not been surprised (much like getting startled because of fireworks, a friend firing a gun, or something of the sort). They could have had readied actions for when the wizards teleported in that would trigger if their initiative precedes the wizards entry.
That is exactly what I would do, yes. They were prepared for the fight, even if they weren't prepared for the fight to come to them so to speak. As such I'd have rolled initiative for them already (or if they were PC's I'd have them roll)
I agree with those who say the townsfolk would not be surprised in the game mechanics sense but, surprised in the literal sense. The Surprise mechanic seems to indicate that the intent of at least one creature from a group of opposing forces wishes to take an action while undetected. Further, the rules state that beings not actively trying to stay undetected through some means, automatically detect each other. If that settles that particular question for you, I'd like to pose another, more commonly occuring conundrum.
Let's say Group A is approaching Group B. Group A is aware of Group B, Group B is NOT aware of Group A. Most of Group A is not hiding their presence and will be detected by Group B. Group A has a Rogue that all of Group B fails to detect. Group B is Surprised even though they are aware of all of Group A's other members.
I have a few ideas to moderate this situation but, it would be some heavy house rules. I'd like to see what others come up with before i post my "solution".
@Wtfdndad My read of your scenario is this:
1) Group B is surprised by the Rogue from Group A only if the Rogue is approaching from an unexpected direction, like the ceiling, the floor, or from behind total cover. Otherwise, why would Group B not anticipate a creature (the Rogue) approaching when they know that Group A is approaching?
2) If combat is initiated only by the Rogue, Group B cannot respond to the Rogue's initial action+bonus action if #1 is true. So long as the rest of Group A is not intending for this to be a hostile interaction and are not aware of the Rogue's aggressive intention, they too are surprised. If they knew of the Rogue's intent to attack but oppose that line of action, they would not be surprised and can act as normal, perhaps shouting a warning to Group B and thereby preventing Group B from being surprised at all.
3) However, if combat is initiated by all or most of Group A against Group B, then I would say that Group B is not surprised. So then everybody rolls initiative, with the Rogue getting a bonus of +3 to +6 depending on the circumstances of their stealthy approach.
And you've just highlighted how I feel surprise rules fail without a surprise round before normal initiative/combat.
For 1, you tell me. This is going to be the most common scenario for a class to deal with that relies on Stealth. For the sake of semantics, if the rest of group a is terrible at Stealth and will fail, it's mechanically the same as not trying to Stealth.
For 2, if the party is in full agreement, they let the Rogue start the engagement by taking ready action and using reaction to do what they plan to do. This however, pretty much contradicts another SA ruling on delaying your turn. If the group is not aware of the Rogue's intent or not in agreement, the Rogue becomes Group C. Then it also becomes a matter of who encounters who first.
For 3, I totally agree.
Now for a second round of mechanical issues. I'm going to use a more simple example. Group A consists of two Rogue thieves called 1 and 2. Group B is a lone passerby. Both Rogues roll Stealth, 1 fails against passive detection by B and 2 succeeds. Initiative finds 1 going first, then B, lastly 2. Yet again SA complicates the situation by saying that "you can be surprised even if your companion aren't, you aren't surprised if even one of your foes fails to catch you unawares."
Adding numerous conditions makes a successful Surprise attack less and less likely. The quoted line means that if even one of you allies fails to Surprise a targets, so do you.
Yes. It is difficult. Because the consequences of being surprised can be catastrophic. Remember that there is a major difference between being Surprised and just not being able to see one or more of your attackers. Surprise means you are caught off-guard, hands away from weapons, defenses down, distracted. So unawares that you can't do anything useful at all - and you are open to an Assassin's devestating auto-crit sneak attack.
In your example of two thieves attacking and one failing the stealth check - well that failure was the cracking twig that literally ruins the surprise attack for both. No surprise for anyone.
That being said, there are still very many benefits to an ambush even without achieving surprise. The hidden Rogue may not surprise the enemy, but it is still hidden; untargetable until discovered and almost guaranteed advantage and sneak damage on first attack. Ambushers tend to have better cover. The DM might see fit to grant advantage on initiative rolls to a group launching such an attack, and so on and so forth.
If you only had 1 attack per turn and could rarely use the defining feature of your subclass as Rogue /Assasin , that would be pretty annoying. There has to be a better mechanical middle ground for the Surprise scenario. I don't even have a Stealth dog in the fight. I'm the Cleric stomping around in heavy armor with no Stealth, dex or anything remotely resembling a quiet approach.
Surprise in 5e is much more specific and less common than previous additions. At least that is my understanding.
For example, just because something unexpected happens, it doesn't mean you are "surprised" mechanically even if you might well be surprised by the turn of events.
Consider two groups where some members of one group are hidden. These members do not get a "surprise" round. No one is surprised since they have possibly hostile opponents and they are aware that something may be happening. Just because some folks aren't noticed doesn't give them mechanical surprise (though they would have advantage on their attacks if the DM rules that they are hidden ... eg a rogue passing a stealth check before combat starts). However, if ANY of the party are noticed then there is no surprise.
The only times I have found where surprise occurs is when one side is prepared for combat and jumps in against an opposing side that is unaware that combat is imminent. This has happened in games I have played where one side sets up a particularly well planned ambush and are not noticed before they start attacking. It also happened when the party jumped through a portal into a room with unprepared enemies.
Other than that, the DM has to rule whether surprise is applicable or not and in most cases it is not.