The old archmage closing the gap in the world that Ged's broken summoning spell had opened. Heroic Sacrifice.
"Ged stepped forward and struck the lord's hand down with his own, saying as he did so only one short word. And though he had no staff, and stood on alien ground and evil ground, the domain of a dark power, yet his will prevailed." In the Court of the Terranon, in Wizard of Earthsea.
Ged holding off an earthquake and the wrath of an ancient evil for over a week in Tombs of Atuan.
In the very first chapter, Ged creates a dense fog to repel an invading army, tricking some of them into riding off a cliff before the rest retreat. The story soon spreads across the country, and he earns his name.
Ged facing down the Dragon of Pendor is probably second only to Bilbo and Smaug when it comes to "dealing with a dragon" scenes. Of course, Bilbo just wanted to get out of there alive; Ged's goals were a bit more ambitious.