The Magic Circle spell creates a circle that protects against certain types of creatures. The spell description states:
Choose one or more of the following types of creatures: celestials, elementals, fey, fiends, or undead. The circle affects a creature of the chosen type in the following ways:
The creature can't willingly enter the cylinder by nonmagical means. If the creature tries to use teleportation or interplanar travel to do so, it must first succeed on a Charisma saving throw.
The creature has disadvantage on attack rolls against targets within the cylinder.
Such a creature, from outside the cylinder, tries to make an unarmed melee attack against a creature fully within the cylinder. What happens?
- They cannot do so, because part of their body entering the cylinder is treated the same as their whole body entering the cylinder.
- They can do so, but have disadvantage. They are not trying to "enter" the cylinder, just briefly extending their body into it.