The sanctuary spell description states:
Until the spell ends, any creature who targets the warded creature
with an attack or a harmful spell must first make a Wisdom saving
throw. On a failed save, the creature must choose a new target or lose
the attack or spell. This spell doesn't protect the warded creature
from area effects, such as the explosion of a fireball.If the warded creature makes an attack or casts a spell that affects
an enemy creature, this spell ends.
The description of the compelled duel spell says (PHB, p. 224):
[…] One creature that you can see within range must make a Wisdom
saving throw. On a failed save, the creature is drawn to you,
compelled by your divine demand. For the duration, it has disadvantage
on attack rolls against creatures other than you, and must make a
Wisdom saving throw each time it attempts to move to a space that is
more than 30 feet away from you; if it succeeds on this saving throw,
this spell doesn’t restrict the target’s movement for that turn.The spell ends if you attack any other creature, if you cast a spell
that targets a hostile creature other than the target, if a creature
friendly to you damages the target or casts a harmful spell on it, or
if you end your turn more than 30 feet away from the target.
If someone has cast sanctuary on me, and then I cast compelled duel on an enemy, does this mean that the creature targeted by compelled duel will have to succeed on at least one Wisdom saving throw in order to take any aggressive action toward the PCs without disadvantage?
Best Answer
No, casting Compelled Duel would end the Sanctuary effect on you.
As you quote:
Compelled Duel is a spell which affects an enemy creature, being cast by the warded creature (you), so it causes the sanctuary effect to end.
You can do it the other way around though
If you cast Compelled Duel and then have Sanctuary cast on you, the effects can overlap. A target successfully affected by Compelled Duel would have disadvantage on attacking anyone but you, but would be forced to make a wisdom save before they could attack you.
Note that the Wisdom save that Compelled Duel mentions happens only once, when you actually cast the spell on them. They either succeed, and therefore shrug off the effect and can act as normal, or they fail, and thus suffer disadvantage on attacks against other targets for the duration of the spell. The subsequent wisdom saves the spell may cause are only to do with the affected creature's movement - it still has disadvantage on attacks even if it successfully manages to move away from you (though you must remember to chase after it yourself if you don't want the effect to end).