Is it possible to gain the benefits of lying prone without incurring disadvantage on attacks? If so, is this broken?

Question

PHB p. 190 says:

You can drop prone without using any of your speed. Standing up takes more effort; doing so costs an amount of movement equal to half your speed... You can't stand up if you don't have enough movement left or if your speed is 0.

The description of the Prone condition (PHB p. 292) says:

An attack roll against the creature has advantage if the attacker is within 5 feet of the creature, Otherwise the attack roll has disadvantage.

Imagine I'm a rogue positioned on a rooftop overlooking the street where the combat will take place. According to these rules, it seems that I can begin the combat prone, and then on each subsequent turn:

• Use half my movement to stand up
• Fire a ranged weapon at one of my enemies below, plus sneak attack if I have any allies in melee with them
• Drop prone again for free, giving disadvantage to any ranged attacks made against me until my next turn, at which point I do this all again.

As long as I'm protected from melee attacks, say by a secure position or an effective tank, it seems like I can permanently give my enemies disadvantage on their attempts to hit me, with no downside. This seems like cheese to me, but I can't find any rule that contradicts it. So my question is twofold:

1. Is there some reason this sequence of moves isn't possible?
2. If it is possible, why is it not as broken as I think it is?

Answer 1

You are describing a sound tactic

(in the game and in the real world)

It has been said that the goal of military action is to take a fair fight, and make it unfair. Most of martial history, from drone strikes to throwing rocks from a high place, has been about giving yourself an advantage. And this is no different.

In the real world, when firing from behind cover, people often drop behind it completely to reload, or between shots. They see no need to expose their body to attack at all times, and instead choose to only become vulnerable when they intend to fire. You can think of this as similar to what your Rogue is doing: they expose themselves to danger when they need to, and otherwise stay prone.

And to claims that this is "cheese," keep in mind that this is tactically similar to using a Rogue's Cunning Action to Hide each round, and can be countered by most things that counter that (Medix2 gives some great examples , like having enemies Ready an action to attack the Rogue when exposed, or doing something that gives Disadvantage to the Rogue's attacks to rob them of Sneak Attack damage). Also, this tactic is not entirely without cost, because going prone every round has some inherent drawbacks.

What you give up doing this

There are two major things you lose with this tactic

1.) You are vulnerable to melee attacks while prone.

If you can get on the roof, then odds are good someone else can too. And as you stated, while a creature is prone (PHB, p. 292):

An attack roll against the creature has advantage if the attacker is within 5 feet of the creature

The higher up or less accessible the roof you're on, the less this is an issue. But you never know when an enemy might summon an ally, or unexpectedly cast the Fly spell, or quietly climb the wall. If you find yourself in melee range while prone, enemies will get advantage on their attacks.

Besides the mechanical vulnerability, you are also likely cut off from your allies. If your rooftop is hard to access, keep in mind that your close-range friends may have trouble coming to your aide. And you'd have some trouble reaching them as well, which brings me to my next point.

2.) You lose some mobility

Your strategy ensures that you lose half your standard movement every turn standing up. This could cause a problem if you need to move far in one round. Combat is dynamic: an enemy may move around the battlefield, perhaps moving out of your range, or into a place that has total cover from your vantage point. If this happens, you may not be able to keep up with them. Your cunning-action Dash makes this less of a problem, but you'll not only have to spend movement to stand up, but also to get down from the top of the roof.

Essentially, the more inaccessible you are, the safer you become, but the harder it is for you to adapt to enemy tactics. That being said, there are a lot of situations where going prone defensively then standing offensively is a great tactic! If you think it will help in your situation, I say "go for it."

Answer 2

This is possible and not broken

No part of the rules prevents the scenario you've described so it does work. Now let's address why it isn't as strong as you think:

1. This requires a very specific kind of encounter environment.

   You must be in an unreachable position, have enough ammunition, and be able to see your opponents who cannot be too far away lest you have disadvantage. You cannot have disadvantage from some source and your opponents cannot have advantage from some source.

2. Your enemies have multiple ways to get around this.

   They can simply move somewhere where you cannot hit them, they can cast fog cloud or darkness to level the playing field and cancel any (dis)advantage on both sides, they can use spells to get to you as well (for example, misty step or even something like summoning a creature right next to you who then attacks you, with advantage). Most importantly, they can simply Ready actions to attack you when you stand up.