Readied actions to intercept projectiles

Question

I'm going to be a first-time DM in a few weeks DMing for some new players who will not necessarily be reading the rules. Because of this, I'm trying to get a good grasp on as much of the free material as possible.

My question is whether or not it is possible in combat to ready an action such as, "If an Archer fires an arrow at our wizard, move in front of them to block the arrow." This seems reasonable because they are simply moving. The Basic Player Handbook states the following for the action Ready.

First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it.

In this case, the trigger is the fired arrow, and the action is movement. So the action seems OK, assuming they haven't used up their movement during their last turn.

My question is, as a DM, should I allow them to intercept an arrow and take damage instead? I think it might be important to say that we will not be using a grid for battle.

I think it wouldn't be unreasonable to have this be a valid action, and that they could take damage in place of the initial target; however, the rules about cover state:

if a target is behind a creature that gives half cover

which gives a character +2 AC and bonus on dex saving throws. Which leads me to believe that this would not be possible.

So I would allow the action to happen, but should it be resolved via cover or via an interception?

Answer 1

Readied actions happen when the trigger occurs, interrupting the initiative order. After the readied action takes place the rest of the action takes place as normal. In the case you mention, it is valid for one player to move in response to an enemy attack to give cover, given that he/she had readied the action (or has an ability that allows him to use a reaction in the same way).

Although I think he would efectively be giving cover to his ally, not taking the brunt of the hit, because the enemy would have been aiming at the ally, not the reacting player. It doesn't make complete sense, but it is that way according to the rules (they are in place to make thing easier and simpler, with as much realism as needed without being bothersome).

Your reacting player would give a +2 to AC to his friend. Then, by optional rules, if the attack doesn't hit the protected ally, but would have hit him if he hadn't the cover (the +2) it hits the cover. In that it would hit the reacting player, but it needs to surpass his AC to damage him.

It is a bit convoluted, so tell me if I need to clean up or clarify my answer.

And, of course, you are free as DM to change anything and allow the reacting player to completely protect his ally despite any rule I have commented ;)

Answer 2

Allow the action, resolve using cover, optionally allowing cover to be hit

As per your own assessment, the action itself is accounted for. Seeing an enemy about to loose an arrow, the Fighter heroically puts himself between the Wizard and the assailant.

The exact timing of the readied action is up to the DM, but I see no reason not to allow it before the arrow is loosed - the player should have been specific about conditions, so the Fighter is specifically looking out for ranged weapons being aimed at his or her ally.

By the base rules for cover, as you rightly put forward, the Wizard now benefits from +2 to AC.

But you can go one step further to create the heroic 'taking the bullet' effect. The Dungeon Master's Guide puts forward the following optional rule for attacks hitting cover (p.272):

When a ranged attack misses a target that has cover, you can use this optional rule to determine whether the cover was struck by the attack. First, determine whether the attack roll would have hit the protected target without cover. If the attack roll falls within a range low enough to miss the target but high enough to strike the target if there had been no cover, the object used for cover is struck. If a creature is providing cover for the missed creature and the attack roll exceeds the AC of the covering creature, the covering creature is hit.

Now, the Fighter may well have better AC than the Wizard anyway; in this case, the attacker will never hit the cover (as it must beat the covering creature's AC). You can maintain the flavour of 'blocking' the attack in this case by simply describing how the attacker failing to hit the Wizard's covered AC is a result of the Fighter's intervention. Maybe a spectacularly low roll is the attacker being put off by the Fighter's bravado and selflessness. Descriptions like this don't need to have any mechanical impact to help immerse your players further into the events of battle.

Answer 3

A brief overview of how Ready works.

Sometimes you want to get the jump on a foe or wait for a particular circumstance before you act. To do so, you can take the Ready action on your turn so that you can act later in the round using your reaction. First, you decide what perceivable circumstance will trigger your reaction. Then, you choose the action you will take in response to that trigger, or you choose to move up to your speed in response to it. - p. 193 - Player's Handbook

The Ready action costs you your action on your turn and can be used to do anything that you would normally do as your action on your turn. Included in this would be to hustle (aka move a second time) which acts as a separate move action from your move on your turn. Beyond that the Ready action explicitly states that moving up to your full speed is always an option when the Ready action trigger goes off.

Additionally always remember that the player needs to have a reaction available (you only get one per round).

The PHB is actually unclear about the resolution order of reactions and their triggers except when explicitly stated such as in the Shield spell text. The only mention of this in the DMG leaves it up to the DM's discretion as to when a reaction occurs (whether before or after) with respect to the trigger.

ADJUDICATING REACTION TIMING

Typical combatants rely on the opportunity attack and the Ready action for most of their reactions in a fight. Various spells and features give a creature more reaction options, and sometimes the timing of a reaction can be difficult to adjudicate. Use this rule of thumb: follow whatever timing is specified in the reaction's description. For example, the opportunity attack and the shield spell are clear about the fact that they can interrupt their triggers. If a reaction has no timing specified, or the timing is unclear, the reaction occurs after its trigger finishes, as in the Ready action. - p. 252 - Dungeon Master's Guide

Cover would apply.

Assuming you as the DM have the reaction complete before the ranged attack trigger finishes the player would impose the half-cover -2 penalty to the attack and nothing else. The attacking NPC is still trying to hit their intended target, nothing the PC can do in the PHB would allow them to do what you are describing except by explicit DM fiat (which is fine and sort of encouraged by the way the books are written).

If you want to build this into the rules, homebrew a Feat.

However if you are looking for a RAW-esque approach I would suggest creating a custom feat similar to sentinel or shield master that would allow a PC to use their reaction to redirect an attack onto themselves (maybe make it a requirement that the target is an ally within 5 or 10 feet of the player.