The hiding sidebar from PBR, p. 60, begins, "The DM decides when circumstances are appropriate for hiding." What does this mean to you?
Many will reply that it means it's the DM's job to determine if you can hide under a given set of circumstances, making hiding a matter of "DM, may I?"
I read it slightly differently. The way I read it, it means it's the DM's job to determine whether or not, and where, to place said appropriate circumstances in an encounter area or an area of exploration, just as it's the DM's job to determine the existence and placement of monsters, traps, treasures, and other elements of the game's fictional world.
But what are the appropriate circumstances for hiding? I think the rule-book tells us pretty clearly what they are.
Here's my list of appropriate circumstances under which you can try to hide:
- You are in an area that is heavily obscured by such things as darkness, opaque fog, or dense foliage.
- You are completely concealed by an object that blocks vision entirely.
- You are obscured by a creature that is at least two sizes larger than you.
- You are invisible.
I would add to the top two above circumstances the requirement that the area or object must be of sufficient size to create uncertainty as to your precise location, or you must not be observed entering the area or getting behind the object by the creature from which you are hiding, whereas invisibility creates its own uncertainty as long as the invisible creature is free to move.
For some characters, there are additional circumstances under which they can try to hide, i.e.:
- You are a wood elf and in an area that is lightly obscured by natural phenomena such as moderate foliage, heavy rain, falling snow, mist/patchy fog, twilight, dawn, or a particularly brilliant full moon.
- You are a lightfoot halfling and obscured by a creature that is at least one size larger than you.
- You are a ranger, 10th level or above, camouflaged as per the Hide in Plain Sight feature, and pressed against a solid surface at least as tall and wide as you are.
- You are a character with the Skulker feat and in an area that is lightly obscured from the point of view of the creature from which you are hiding.
Because these characters can hide under conditions which would otherwise allow them to be seen, I would stipulate the additional requirement that they are not being directly observed by the creature from which they are trying to hide while becoming so hidden.
Of course the DM is also free to determine what colorful details attend such circumstances. For example, while many seem to consider darkness absolute, because it blocks vision entirely, clearly there are many moonlit nights that are not so dark but which would still be considered to impose the condition of darkness.
Hiding is also possible while travelling at a slow pace under any of the above circumstances that apply, which for most characters would be travelling through heavily obscured areas such as a dense forest, thick fog, or under cover of darkness.
What circumstances do you consider appropriate for hiding?
So I think that if the players can give me a reasonable explanation of how they are attempting to hide, then they can make an attempt. That chance can be modified, usually by advantage/disadvantage, but sometimes more severely if it's really a long shot.
So in most combat situations, you'd have disadvantage on your Stealth check and/or they will have advantage on their passive Perception check.
However, if another character used the Help action to create a distraction, then you could attempt it normally. Probably not with advantage, as the advantage caused by the Help action negates the normal disadvantage.
Likewise, I'll go to the rock in the middle of the field.
If you're behind the rock, they know where you are. But the definition of hidden in the game isn't "they know where you are," it's unseen and unheard.
So here's how I handle those situations.
First, you
can attempt to hide. It may or may not be with disadvantage or they may have advantage on their Perception check (they know where you are after all).
If you're successfully hidden (either from a successful attempt in the prior round, or you're a rogue that used your Cunning Action as a bonus action first), and your turn occurs before the target, then you are unseen and have advantage on your attack. You are no longer hidden, though and must attempt to hide again.
Why? Because your Stealth check had already succeeded. They know you'll be coming out, but their reaction is mistimed (like Whack-a-Mole).
If, however, their turn happens first, then they can either use their action to make a Perception check, they can do something else, like move to where they can see you, or they can Ready an action to, say, shoot you with an arrow when you pop out. At this point, you're still hidden, but as soon as you pop out, you are no longer hidden because their reaction interrupts your action, and thus they have seen you and you are no longer hidden.
Now here's where it gets even more interesting. If you are hidden behind a wall that has a peephole and you can see them, then this doesn't work. But if you're hiding behind a rock, and they cannot see you, then there is also a chance that you cannot see them. So they could potentially hide from you too, and Ready their action to shoot you with a bow and they will have advantage.
See, it all comes down to a few questions:
Are you in a position where you can be unseen and unheard? If yes, then you can attempt to hide.
Most of the time, your Stealth attempt is made against their passive Perception (unless they want to use an Action to make it).
Once you have successfully hidden, can they change that fact before your attack?
If you're already hidden at the start of your turn, and they can't change that fact, then you have advantage on your attack.
The only circumstance I can think of mechanically that changes that is for them to Ready an action for when you pop out.
Otherwise they have to do something that breaks your hidden state. In other words, if their turn occurs first, they must use an Action to make a Perception check that breaks your stealth (which would be against your passive Stealth as far as I'm concerned), or they move to where they can see you, etc.
It's important to understand that there is really no mechanical benefit to being "hidden." The mechanical benefit of advantage on your attack roll is tied to being unseen. So you don't need to be hidden (which is both unseen and unheard), just unseen. Like a drow with 120' darkvision against an elf with 60 feet. The drow would also have advantage on Stealth checks to hide, but they don't need to hide, they already have the benefit granted while remaining unseen.
So when you "hide" behind a rock in the middle of a field, you're probably not fooling anybody as to where you are. But, you can take advantage of the fact that you can't be seen, and that they will have to react to you popping out at an unexpected interval of time. Of course, they might very well have advantage on their Perception checks to prevent this from happening.