Understanding Cover and Hiding in 'Dungeons & Dragons'
One of the most misunderstood rules in Dungeons & Dragons involves the use of cover and how to hide while in combat.
A Rogue darts in and out of a battlefield in Dungeons & Dragons, striking a distracted enemy with her twin blades before searching for a hiding place. She darts behind a rocky outcropping and then declares that she's using her bonus action to hide. This simple scenario has happened thousands of times during a Dungeons & Dragons session, but many players (and DMs) don't quite understand the mechanics that determines what advantages a rogue has for hiding in the middle of a battlefield.
With the release of its Fifth Edition ruleset several years ago, Dungeons & Dragons simplified many of its mechanics in a way that promoted narrative choices over a strict adherence to rules. Set attack bonuses were mostly replaced with granting advantage or disadvantage on attacks rolls, and attacks of opportunity and flanking were simplified or turned into optional rules.
One mechanic that retained the set bonuses of older editions involved players who used cover while dodging ranged attacks. A player can position themselves between obstacles (or even party members) to grant them a fixed AC bonus while in battle. The actual rules regarding cover are simple - a player receives a +2 bonus to their AC and Dexterity saving throws while behind half-cover, they receive a +5 bonus to AC and Dexterity saving throws behind three-quarters cover, and they can't be directly targeted by an attack or spell while behind total cover.
However, the interpretation as to what constitutes a certain kind of cover (especially half-cover and three-quarters cover) is when things get tricky. These decisions are often left to the discretion of a DM, which can lead to arguing and pleading when a player wants to hide behind something in battle. At least in my games, hiding behind something is usually considered half-cover, unless the DM specifically says otherwise.
Another tricky part about cover rules is that party members and enemies can also count as "half-cover." If you're standing in the rear of the party and someone shoots an arrow at you, the rules do allow for you to gain a half-cover bonus. There's technically no penalty for using one of your party members as cover, although Dungeons & Dragons does include variant rules that allows a DM to "hit cover" when an enemy attack misses because a player is hiding behind another party member. The variant rules state that if an attack misses because a player is using a creature (either friendly or enemy) as cover, the DM can compare the attack roll to the AC of whatever creature is being used as half cover. If that attack exceeds the AC of the creature being used as cover, it hits that creature instead.
The other misunderstood mechanic involves hiding on the battlefield. Players (and monsters, too) can choose to use a Hide action during battle, which allows them to make a Stealth check to stay hidden on the battlefield. Some players (usually rogues) interpret hiding as a way to basically disappear in battle, allowing them to Sneak Attack the same enemy over and over again, as they can use their Cunning Action ability to hide without using their action during combat.
However, hiding in combat is a tricky mechanic, a deliberately grey area left to the DM to adjucate on a case by case scenario. In a 2017 podcast, Dungeons & Dragons rules designer Jeremy Crawford discussed some of the nuances of hiding in battle, specifically when it comes to rogues and their Cunning action ability. If a player hides in combat, but then moves to make an attack, they are no longer considered hidden. Stabbing someone in the back with a knife might work once, but they'll likely expect a second knife attack even if a player hides in a bush between attacks. Likewise, there's nothing stopping a bad guy from chasing a rogue during their turn or trying to find the rogue's hiding spot.
However, a player can attack from a distance and retain the benefits of hiding even after making an attack...provided they stay unseen and unheard. Whether this means moving positions after making an attack or having a special muted weapon is once again left up to the DM's discretion. Remember that most enemies aren't going to just stand around and die either. If they feel that the rogue is the biggest threat, they can ready their actions to shoot back at a rogue whenever he pops up to make an attack.
Of course, the easiest way to figure out how cover and hiding works is to having a discussion with your DM. Ultimately, the DM's decisions overrule Dungeons & Dragons' rules, as they're the ultimate referee in combat. While a DM shouldn't try to nerf a player's abilities in combat (especially if they're a rogue that relies on sneak attacks to do the bulk of their damage), they should also make their positions clear and work out ways to both showcase and challenge a player's abilities in and out of combat. Hiding shouldn't make a player invisible, but it also shouldn't be taken out of a player's arsenal of tricks either!