Does mounted combat require a willing rider as well as mount?

Question

The Mounted Combat rules say...

A willing creature that is at least one size larger than you and that has an appropriate anatomy can serve as a mount, using the following rules..."

This requires that the mount be willing, but it does not say whether the rider has to be willing.

Some instances in which a rider might be unwilling could include:

• If the rider had been grappled and carried by a creature that otherwise met the definition of a mount

• If the rider began as willing but the mount was later charmed, polymorphed, frightened, or had some other change of condition such that the rider no longer wished to be a rider but had not yet had their turn and so could not dismount

• If the rider was incapacitated or rendered unconscious and so could no longer give their consent as a willing rider (but by DM's decision could physically remain on the mounted creature)

[Note for the first possibility: The grappling rules say...]

When you move, you can drag or carry the grappled creature with you [...]

[Note for the last possibility: the "Mounted Combatant" Feat explicitly requires that the rider not be incapacitated to use the feat, but the Mounted Combat rules do not]

In any of these cases, would the removal of the rider's willingness to be mounted mean that the rider would no longer be treated as being in mounted combat, even if they had not yet had the chance to dismount?

In particular, would an unwilling rider still suffer opportunity attacks if moved by the mount on the mount's turn?

The opportunity attacks rule says...

You can make an opportunity attack when a hostile creature that you can see moves out of your reach. [... But you] don't provoke an opportunity attack when you teleport or when someone or something moves you without using your movement, action, or reaction.

But the mounted combat rules say...

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

Answer 1

Both parties need to be willing, but that's not all

All rules regarding mounts require

A willing creature that is at least one size larger than you and that has an appropriate anatomy. (1)

Once you've determined whether the mount is willing,

Once during your move, you can mount a creature that is within 5 feet of you or dismount. Doing so costs an amount of movement equal to half your movement speed (1)

The Fighter did not mount the Ogre. Regardless of her agency, it didn't take place on the Fighter's turn and she didn't spend any movement.

Dismounting the hard way

When knocked unconscious, a creature...

drops whatever it's holding and falls prone. (2)

Per mounting rules,

If you're knocked prone while mounted, you must make the same saving throw (1)

which, as described in the previous sentence, says

you must succeed on a DC 10 Dexterity saving throw or fall off the mount. (1)

When unconscious, a creature

automatically fails Strength and Dexterity saving throws, (2)

so the Fighter falls off the Ogre and, to what would be her profound relief were she still conscious, is no longer susceptible to mount-based Attacks of Opportunity

What you've written could happen

The Fighter could intentionally mount the Ogre during her turn - e.g, climb onto its shoulders or back for a better stranglehold - and spend movement while doing so. The Ogre could allow this to happen so that it fits the "willing" descriptor, thereby fulfilling all remaining mounting criteria. On the Ogre's turn, it could run the Fighter past the orcs, provoking attacks of opportunity.

Intelligent creatures, such as dragons, act independently (1)

If the Ogre is smart enough to try this, let alone its capacity for rules-lawyer arguments, it's definitely intelligent.

An independent mount retains its place in the initiative order. Bearing a rider puts no restrictions on the actions a mount can take, and it moves and acts as it wishes. (1)

The Ogre can absolutely run the her past the Orcs on its turn.

If the mount provokes an opportunity attack while you're on it, the attacker can target you or the mount. (still 1)

Regardless of the whole "Hostile" argument, the Ogre is now mounted by the Fighter, and the Orcs can therefore choose to target the Fighter

Excessive citations:

(1) PHB Chapter 9, p.198

(2): PHB Appendix A, p.292

Answer 2

The PHB section “Mounted Combat” presupposes a willing rider. This section states that a mounted rider can dismount for half their speed, can use a reaction to dismount if their mount is knocked prone, and can choose to control a(n unitelligent) mount. A creature that cannot do such things is therefore not acting/able to act in a manner consistent with this section. While such a creature may still be mounted, it is not mounted in a manner that subjects it to the Mounted Combat rules.

There is no set of rules that applies to a creature mounted against its will. At this point, a DM will have to rule what happens. Repurposing the rules about willing riders does seem like a fair call, but again, it is outside the scope of RAW.

There is no rule that allows opportunity attacks on a forcibly mounted rider. A forcibly mounted creature, being outside the Mounted Combat rules, is not subject to the Mounted Combat rule that opportunity attacks can target the rider. There being no specific rule, the default rule still then applies: a creature moved against its will cannot be the target of an opportunity attack.

Of course, given that forcibly mounted activity is undefined, a DM could still rule that a forcibly mounted rider is subject to opportunity attacks. The rules do not forbid opportunity attacks; they merely do not allow them (because they have not allowed for them).

There is no rule allowing opportunity attacks on an unconscious rider. The unconscious condition drops its subject prone and induces automatic failure on Dex saves. A willing, unconscious rider therefore falls prone, automatically fails the Dexterity save to stay on their mount, and falls off. Meanwhile, an unwilling/forcibly mounted rider is still subject to the above. Either they were never subject to opportunity attacks, or the DM is having to make up their own rules about what happens.

How could this work in RAW/without DM fiat/more cleanly in general? Ogre grabs fighter, then runs through orcs, who have held the Attack action for trigger: fighter in melee range. It's a fun scenario! I'll probably try and use it at some point.