What spell is this?

[Norfleet]

That's Seeking Arrow: It does 10-15 points of armor-piercing damage. You can defend against it by filling the targetted province with scout chaff, being sufficiently heavily armored that the arrow is unable to penetrate your armor, wearing a robe of missile protection, being lucky, or just being really buff: Regardless, if the arrow hits you, you receive a chest wound. This can often be a good enough reason to use it on targets even if you know they're too buff to actually die outright.