I've heard the argument that magic in Middle-earth is generally subtle, and many D&D spells wouldn't fit in the setting. While that is true, there are exceptions. Gandalf doesn't often display his power in The Hobbit and Lord of the Rings. However, there are times he has used his magic in combat.
This passage is from The Hobbit, in the chapter “Out of the Frying-pan into the Fire”.
He gathered the huge pine-cones from the branches of his tree. Then he set one alight with bright blue fire, and threw it whizzing down among the circle of the wolves. It struck on on the back, and immediately his shaggy coat caught fire, and he was leaping to and fro yelping horribly. Then another came and another, one in blue flames, one in red, another in green, They burst on the ground in the middle of the circle and went off in coloured sparks and smoke.
This passage is from The Fellowship of the Ring, in the chapter “A Journey in the Dark”.
Stooping like a cloud, he lifted a burning branch and strode to meet the wolves. They gave back before him. High in the air he tossed the blazing brand. It flared with a sudden white radiance like lightning; and his voice rolled like thunder.
'Naur an edraith ammen! Naur dan i nguarhoth!' he cried.
There was a roar and a crackle, and the tree above him burst into a leaf and bloom of blinding flame. The fire leapt from treetop to treetop. The whole hill was crowned with dazzling light.
Are these examples proof that the Fireball spell exists in Middle-earth (albeit with different spell components), or would another spell be more appropriate?
Here's the scene in question from the first Hobbit movie: