In Chapter 4 what happened when Ged was in the courtyard?

While everyone else was busy celebrating Moon's Night, Ged and Jasper get into an argument over who has the greatest power. Ged challenges Jasper to a duel, and Jasper then issues his own challenge at Roke Knoll. The incident ends with Ged's conjuring of the shadow and its subsequent attack on him. The Shadow now roams the world.