The Path of the Ancestral Guardian barbarian's Ancestral Protectors feature (XGtE, p. 10) says:
While you’re raging, the first creature you hit with an attack on your turn becomes the target of the warriors, which hinder its attacks. Until the start of your next turn, [...] when the target hits a creature other than you with an attack, that creature has resistance to the damage dealt by the attack.
Do the party members get resistance to the damage? Or because it specifies "attack", and a fireball (and toll the dead) is not described as an attack, do they take full damage?