Is the Mounted Combatant feat's ability to redirect an attack at the mount limited by the reach of the attacker?

Question

The second benefit of the Mounted Combatant feat says (PHB, p. 168):

• You can force an attack targeted at your mount to target you instead.

My DM used a foe to attacked my mount. Imagine this was the battlefield (seen from above); I was on the C, my mount is large (A), and the monster is M:

# # # # # # #
# # # A C # #
# # # A A # #
# # M # # # #
# # # # # # #

When I said "I deflect the attack to me," the DM said "But the foe does not reach you, which means you can't pull the attack to yourself." That got me thinking. I'm wanting to know how this works in this situation.

How does the attacker's reach interact with Mounted Combatant's ability to force an attack against the mount to target the rider instead?

Answer 1

You are probably correct...

The second bullet point of the Mounted Combatant feat reads (PHB, p. 168):

You can force an attack targeted at your mount to target you instead.

This does not provide any qualifications such as "...if it can reach you." or "...if the attacker can see you," etc. The feat says you may redirect the attack, full stop.

Mechanically, this makes sense. Imagine a humanoid mounted on a dragon or something so large that the humanoid would never be within reach from a melee attack from any direction but directly above. Such a mount would mean the second bullet point of the Mounted Combatant feat would almost never be usable.

I think it's important to point out that the rider has the agency to redirect the attack. It is not a case like the spell sanctuary where the attacking creature has to save against some sort of an effect. Nor does it work like the Cavalier fighter's Unwavering Mark or the Ancestral Guardian barbarian's Ancestral Protectors features, where the attacker is incentivized (but not mandated) to choose a specific target.

The text doesn't provide any sort of narrative description to help describe how this feature manifests but what it seems to be attempting to simulate is the rider's ability to shift her position in the saddle to place a part of her body in the way of the incoming blow. I say "shift" because no movement is spent as a part of this feature.

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...But the DM is allowed to be more correct

However, at the core of D&D 5th edition is what is colloquially called "Rule Zero", which grants the DM the power and responsibility to be the final arbiter at the table. It's found in the intro to the DMG (p. 4), under "The Dungeon Master":

The D&D rules help you and the other players have a good time, but the rules aren't in charge. You're the DM, and you are in charge of the game.

And also touched upon in the intro to the PHB (p. 6) and basic rules, under "How to Play":

2. The players describe what they want to do.
3. The DM narrates the results of the adventurers' actions.

I can imagine a situation where a person is riding a colossal mount. Something the size of a three-story building. The rule for the Mounted Combatant feat allows the rider to redirect an attack targeted at her mount to the rider instead. How could a rider three stories up possibly interpose her body against an attack being made down at the ground level?

The letter of the rule departs from reasonable imagination completely in this situation.

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So the answer is best summed up as: the rider can redirect an attack to herself even if doing so would cause that attack to extend beyond its normal reach/range unless the DM decides that this is not feasible. In this case, what the DM says happens is what happens.

Answer 2

A bit of a frame challenge here... If your DM requires that square layout you drew, your DM is looking at positioning too rigidly.

From Creature Size

A creature's space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn't 5 feet wide, for example, but it does control a space that wide. If a Medium hobgoblin stands in a 5‐foot-wide doorway, other creatures can't get through unless the hobgoblin lets them.

Creatures are not static in combat, they're constantly moving and shifting within their space. A horse is not ten feet long and ten feet wide; a creature's size is the space it controls, not how big it is. A horse represents a lot of mass moving around in that space. In a similar fashion, a giant constrictor snake's body shape is clearly not laid out to cover a 15'×15' square. When coiled up to allow for a solid base and striking potential, that 15' square becomes the space it controls, but it still doesn't cover the whole area.

So, if a large creature doesn't actually fill the whole space, it's doesn't make much sense that you have to declare the rider to be on a specific square of that space. A rider on horseback is pretty much in the physical center of the mount. Over the years, I've found the best, least complicated, fastest playing way to manage mounts (without sacrificing too much verisimilitude) is to consider the rider to be in any and all spaces the mount is.

Answer 3

You are absolutely correct in that the feat allows you to redirect the attack to yourself without any riders on reach. We can argue about how illogical that is, but that is one of the powers that the feat that you have invested in gives you.

Nevertheless, there is enough leeway in the interpretation of the rules that your DM is fully justified in setting some conditions. So I would always go along with the ruling of the DM, and I do not disagree with the ruling as made.

Nevertheless, I would like to give some hints as to how I would handle the situation as DM as a possible alternative that works for me. (You do what works for your table and for the enjoyment of your players.) As DM, I am the full master of the monsters I have placed in my playground for the benefit of my players. I am therefore already master of the meta-game and do not need to fall into rules traps. If my player has invested in the Mounted Combatant feat, I am not going to nerf it by adding my own conditions. Instead, I will not have my monsters target the mount in the first place if the rider is out of range, since I know that it would be an oversight for the rider NOT to redirect the attack in that case. Instead I just have the monster move to where the rider IS within range and then attack the rider. Then I do not need to make any awkward rulings.

This gets more interesting if, say, the mount blocks a hallway so that my monster is unable to move around it to hit the rider. In that case, I would just have my monster use the Tumble or Overrun action/bonus action from page 272 of the DMG, and then hit the rider from the back side.

On the other hand, if the mount is huge or larger so that I cannot reposition the monster to hit from the other side either, then as DM I have the power to define the mount as "suitably large" to use the "Climb Onto a Bigger Creature" option in the DMG. Now if my monster is too large to climb onto a Huge or larger mount (and as DM I would let a Large monster attempt to climb a Huge mount, knocking the Medium or smaller rider out its way), then it is only one of a small handful of Huge or larger monsters with insufficient reach or a ranged weapon to hit the rider anyway without needing to climb up. I would therefore ask myself "Why did I put this odd creature into my playground?" I can just swap it for an alternative creature with reach or a ranged attack if this is going to be an issue.

These different approaches add some action and dynamism to the encounter and makes combat a lot more fun for the players. I try to build up the epic nature of the narrative. I would have my creatures move, tumble, overrun or climb the mount to dazzle my players with some action. This for me beats having my creature just stand there targeting the mount when the Mounted Combatant rider is out of range, forcing me, the mighty DM, to make an awkward and unnecessary ruling. I never have to put myself into that position.

Anyway, this is just my alternative to nerfing a feat. As always, you do what works for your table.

Answer 4

If the attack can reach the mount, it can reach the rider

Unfortunately, the optional "combat on a grid" rules do not define well "where" a rider is on a mount. DM's will have to make their own decisions about positioning, and in this case your DM decided that you were on a 'corner' of the mount, the 'far corner' from the foe. This should make you out of range for a normal attack from that foe. There is no rule that says, 'When you take the Attack action, if you can target a mount, then you can target its rider instead.'

However, there is a rule that says nearly that. In the Mounted Combat section of the PHB, we see that:

...if the mount provokes an opportunity attack while you’re on it, the attacker can target you or the mount.

This rule makes no exceptions for reach or positioning. So in the situation you describe, had your mount moved directly away from your foe, at the point in time when it was moving out of your foe's 5' reach, you would have been at 15'+ feet away from it, and it still would have been permitted to make an opportunity attack on you if it chose to, and without you being able to prevent it.

If you have invested in a Feat and are actively trying to take the foe's attack at a closer distance, it is only fair that you should be allowed to do so, when a longer-range attack can still hit you against your will. Now, if your DM has already said that the way they run positioning and reach requires that the rider is in reach for a foe to make an opportunity attack on them as well, then at least they have an internally consistent system, and you should just accept that is how things work in their game, Feat notwithstanding.