If a creature is forced to make a Dex save but has nowhere to go to avoid the effect, can they still make the save?

Question

So I came across a question I had as a DM the other day:

If there is a creature or creatures subject to an spell or effect requiring a Dex saving throw, but they are in a position where avoiding the effect would be impossible, can they still make the save?

The specific situation I was thinking of was as follows.

There are two wizards versus a medium creature. One wizard casts delayed blast fireball, and on the next turn, the other wizard casts either wall of force or forcecage around the creature. When the fireball goes off, the creature will have to make a save to avoid a 20-foot blast inside a 20-foot sphere. There does not seem to be a logical or realistic way the creature could avoid the damage.

I'm looking for input from other DMs or people with heavy experience in the wording of the rules.

Answer 1

Unless specifically stated, a dexterity save doesn't require you to be able to move from your spot

There are undoubtedly some specific effects which provoke Dexterity saves that then allow movement to escape an area (none spring to mind immediately), but that is a specific exception rather than a general rule for saving throws regarding areas of effect. Normally, a Dexterity save does require that you're capable of "movement" - i.e. you're not paralysed - but not that you actually move out of the area.

What exactly that means narratively may vary a lot from effect to effect. In the AoE of a fireball, for instance, a successful Dexterity save might mean that the character hunkers down behind their shield, deflecting some of the fiery blast; it might mean they drop flat to the ground before the fire hits them, narrowing their profile and so avoiding the full force of the spell; it might mean they are simply able to step to the side so slightly into a spot in the area where the flame is less intense (fireball is a fiery explosion, but nothing says that the fire it produces is perfectly evenly distributed through every cubic foot in the area of effect).

Quoting SevenSidedDie from another question, because though it's not a strict duplicate, their answer does address this point very well too:

How do you picture normal save-for-half-damage working? Whether you imagine it as flinging themselves into exactly the right spot to avoid the brunt of the effect; or rolling with the effect so that they blunt its force; or ducking and covering just right so that the worst of it rolls off them like water off a duck; or some kinds of semi-magical ability to deflect area damage; or just a genre trope where they inexplicably always seem to escape unscathed from things that should not be survivable — that's how a rogue evades too, just better.

...

(Note that vitriolic sphere isn't a literal 20′ sphere of liquid acid. It's a 1-foot sphere that explodes, splattering everything in a 20′ sphere. It's much less inexplicable to imagine someone miraculously avoiding all injury from that than from being submerged in a giant ball of acid.)

Answer 2

There are ways to explicitly hamper Dexterity saving throws through limiting movement...

There is precedent for this in existing conditions:

• Creatures who are Petrified, Paralyzed, Stunned, or Unconscious automatically fail Strength and Dexterity saving throws.
• Creatures that are Restrained have disadvantage on Dexterity saving throws.
• The DM is also directly encouraged by the rules as written to apply advantage or disadvantage if they feel the circumstances warrant it.

... but the given examples might not be enough.

Regarding the specific examples, neither forcecage nor wall of force impose these conditions or otherwise directly affect Dexterity saving throws.

Nothing stops a DM from ruling that getting physically trapped within the area of effect would impose disadvantage or force failure on Dexterity saving throws, but this would be a ruling, not a rule.

Answer 3

By the rules, they can still reduce/avoid the damage.

According to the rules, both RAW and RAI, as long as your character is capable of reacting or moving (aka not affected by the Paralyzed, Petrified, Stunned, or Unconscious conditions), they are able to succeed on Dexterity saving throws. Not only that, but should they have the Evasion feature they can even avoid the totality of the damage directed at them. A good example of this is Viari in Acquisition Inc., who famously evaded a fireball that had filled an entire room. Now if you want to make sense of this, it'd be a good idea to look at how Dexterity ST work.

A dexterity saving throw means that through some level of agility or rapidity of action you can avoid a harmful effect. If we imagine this as moving out of the way, then we can interpret this as a character doing the following:

• Avoiding a projectile, debris, or a splash of some harmful substance.
• Moving behind some form of cover.

We can also consider this as the character being quick enough to either block part the effect or reduce its impact by:

• Catching or deflecting the source of damage (this would particularly apply to a Monk defending against Conjure Volley).
• Positioning themselves in such a way that they are less exposed to the effect (turning sideways, laying on the ground, etc).
• Reducing the damage by moving with whatever hits them (like a boxer rotating their head to reduce the impact of a blow).

Apart from positioning themselves in an optimal manner, this is much easier to visualize when we talk about something like shrapnel or debris that must be avoided, but becomes a lot more abstract when a spell that fills an area, in this case a fireball, is concerned. In this case, it may be better to rethink about the spell effect itself rather than the save. In the case of delayed fireball, the spell is seen as

[...] an explosion of flame that spreads around corners.

The explosion can manifest in different way. The fact that it spreads around corners discredits the idea that it's like a shrapnel grenade shooting off a multitude of firebolt-like projectiles, but it doesn't specify that the entire area is uniformly filled with fire. Indeed, it mentions that the fire spreads. Perhaps it does so in a manner that leaves some openings not filled by fire, or perhaps not all of the fire is equally as hot, much like a candle is hottest an inch above the wick. This could be how one avoids or reduces the damage caused by the spell.

Answer 4

If the creature has enough space to fight without disadvantage, it has enough space to make dexterity saving throws without disadvantage as well. However, if the creature is squeezed into a space that is smaller than the space it normally can control, it makes Dexterity saving throws at disadvantage:

Squeezing into a Smaller Space: A creature can squeeze through a space that is large enough for a creature one size smaller than it. Thus, a Large creature can squeeze through a passage that's only 5 feet wide. While squeezing through a space, a creature must spend 1 extra foot for every foot it moves there, and it has disadvantage on attack rolls and Dexterity saving throws. Attack rolls against the creature have advantage while it’s in the smaller space.