-- The (above) is wrong isn't it ? Isn't that exactly what hiding is for. If you duck around a tree/corner or if you are a halfling (that big tall human).. if your Stealth roll beats the enemies passive perception you gain advantage on your first attack roll ?
Here's the relevant quote from the Basic Rules document:
Basic Rules said:
You can’t hide from a creature that can see you clearly, and if you make noise (such as shouting a warning or knocking over a vase), you give away your position. An invisible creature can’t be seen, so it can always try to hide. Signs of its passage might still be noticed, however, and it still has to stay quiet.
In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the Dungeon Master might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack before you are seen.
That's all there is about hiding in combat. The direct reading says that the orcs will see you as soon as you come out from behind the boulder, unless you're Invisible, because creatures in combat stay alert for danger from all directions. There is
some room for interpretation from the DM, if you want to argue that your allies are creating enough of a distraction to make them
forget to check over their collective shoulder to see you coming, but that seems like a pretty big stretch to me. The easier ruling, which seems better supported, is just that hiding in combat is only good if you plan to stay hidden - you
can't use it to gain combat advantage
during combat, so don't even bother. You could probably make a pretty good case
if the orcs didn't know you were there, but I can't imagine them falling for that trick more than once; if they see the rogue vanish from combat and then reappear unexpectedly, there's no way they'd forget about him again.
The tricky part comes with halflings and elves, who have racial abilities that let them hide without being fully obscured. A halfling can be hidden behind the fighter, even though the fighter doesn't fully obscure the halfling - meaning that the halfling can still see the orc and doesn't need to come out from behind the fighter in order to make an attack.
It's kind of like a one-way mirror, where the halfling can see the orc but the orc can't see the halfling, even though the only thing between them is the fighter. At least, that seems to be the common consensus. Personally, I would probably say that the halfling has to come out from behind the fighter in order to get a clear shot, for the sake of simplicity and a consistent narrative.
