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