Can an immobilized character change their facing?

Question

Some effects, such as that produced by the web spell, can immobilize a character or otherwise reduce its movement to 0. In these cases, are characters able to change their facing normally, or are they held in the same orientation they had when immobilized?

The context for this is that a sentry was immobilized while facing away from a given direction. The player argued that their character should be able to sneak up behind the guard despite lighting conditions because the guard could not physically turn to see the player character approaching, so they should only have to move silently and ignore hiding.

Answer 1

Without using variant facing rules, facing isn’t a thing that exists. It never matters which way a character is described as facing, they always have 360° vision (and ability to defend themselves from any angle, or attack into any angle, etc. etc.).

Any deficiencies in vision, defense, attacking, etc., are always handled with some explicit condition. For instance, if someone cannot see around them well or cannot easily move to face a threat, they might lose their Dexterity bonus to AC. If an effect doesn’t state that it has some effect like this, then it doesn’t.

In other words, web apparently can keep you from moving out of a 5-foot square, but it can’t keep you from turning around, moving your limbs, and so on. You can carry this through to any other effects that immobilize: while they hamper movement considerably, they still allow some movements: the only thing they prevent (barring other conditions beyond the immobilizing) is moving from one 5-foot square to another. Contrast immobilization with, say, paralysis, which is what your player’s idea would turn web into.

Answer 2

There is no facing by default

Facing is an optional rule in D&D 3.5. You can see this from it being a variant rule, that is introduced as follows:

The standard d20 combat rules intentionally ignore the direction a creature faces. The rules assume that creatures are constantly moving and shifting within their spaces, looking in all directions during a fight.

Because there is no facing, there is no effect of being immobilized by web on facing.

It would be up to the DM to decide if you can or cannot change orientation if stuck in a web for other purposes.