The Skirmish in the Courtyard was a brief engagement between the Hogwartians of three and the Death Eaters attacking the courtyard from the Viaduct. Though the Hogwarts students managed to hold back the attacks, explosive spells raked the vicinity and forced the three students to retreat to the courtyard.
Prelude
After Harry Potter was supposedly killed by Lord Voldemort in the Forbidden Forest, his body was carried back to the Hogwarts grounds by Rubeus Hagrid. However, once Neville Longbottom took out the Sword of Gryffindor from the Sorting Hat, the second part of the battle began. Harry, only wounded and playing dead, leapt out of Voldemort's arms and ran into the castle. Voldemort and many Death Eaters flew into the castle. While the troops under Voldemort fought against the defenders in the castle, Ginevra Weasley and two other people defended the Viaduct Courtyard.
Battle
Ginny and the Ravenclaw boy and Hufflepuff girl tried to stop the Death Eaters from attacking the courtyard. They apparated into the area, and began shooting violent spells across the field. There was much cover because of the debris of beams, pillars, and the antebellum stone walls. As the attacks were stalled, the Hogwarts students defeated all of the attackers. Shortly after, another wave of attackers came. And then another came. Both shared the same fate: wrecked. Despite the good job having been done, Death Eaters launched bombardments of the area and forced the Hogwarts students to rush inside the building.
Aftermath
When Ginny entered the Great Hall, Bellatrix Lestrange shot a killing curse that missed her by a shot. Molly Weasley intervened, the two dueled to kill. Bellatrix was petrified and then torn into ashes.