Can you Hide from some but not all enemies?

Question

One of my players is asking if he can use Wall of Fire to block off the line of sight of enemy archers. The spell description says the wall is "opaque", so this seems like a valid thing to try.

However, because this opaque wall would make both sides unseen from each other, the advantage and disadvantage would cancel out, and it would provide no immediate tactical benefit.

When you attack a target that you can’t see, you have disadvantage on the attack roll.

When a creature can’t see you, you have advantage on attack rolls against it. (PHB p. 193-4)

In the interest of trying to see if he can get any tactical benefits out of this - if he blocked the line of sight of the enemy archers in a group but not that group's melee fighters, would he/others be able to take the Hide action from the archers even if the melee fighters could still see him?

If he can Hide in this way, that would mean the archers would no longer be able to know his precise position and would need to guess his square before making an attack.

Answer 1

You can hide from the archers separately to the melee fighters

From PHB pg. 177:

Hiding

When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check’s total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.

You can’t hide from a creature that can see you, and if you make noise (such as shouting a warning or knocking over a vase), you give away your position.

When you hide, you make a stealth roll. This is against the passive perception of the enemies you are hiding from. If some have higher passive perception than others, and your stealth roll happens to land in between, you will be hidden from those with lower passive perception but not hidden from those with higher passive perception.

Passive Perception. When you hide, there’s a chance someone will notice you even if they aren't searching. To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creature’s passive Wisdom (Perception) score, which equals 10 + the creature’s Wisdom modifier, as well as any other bonuses or penalties. If the creature has advantage, add 5. For disadvantage, subtract 5.

So, this sets the precedent for being able to hide from some but not all enemies. If the archers cannot see you, you can hide from them, but the melee fighters can see you and thus you cannot hide from them. The fact that the melee fighters can see you does not stop you from attempting to hide from those who cannot see you.

Answer 2

The rules don't cover ranged attacks into a mixed group they can't see, so we can not make a RAW or RAI judgment on the situation other than advantage and disadvantage cancel. So, what is the benefit of casting a Wall of Fire? To keep the game fun, we need to consider what makes sense. Either the archers are guessing at the locations, or firing in the direction of sounds they hear. As a DM I would apply the following rule:

RAF

Melee combat is pretty noisy, hiding would be difficult. However, if the archers are targeting based on sound, I would give a chance that they hit a friendly unit instead of an enemy. There are two was to do this.

1. pool together all creatures engaged in melee combat. Roll a die to randomly choose the archers target (friend or foe).

2. If the ranger's target is involved in melee combat, there is a 50% chance that he targets friend instead of foe.

I would rule that characters not in melee combat could attempt to conceal their location (hide).

Also, in realistic combat, the archers generally stop shooting when the melee fighters engage to avoid hitting friendly units. Possibly make a Wisdom check. A success means they stop firing, a fail means they continue to shoot with the above chance of hitting friendly units.