Durning the Quidditch World Cup, Harry is accosted by Draco on the way to the box-seats. Lucius smirks, nods at Draco, and begins distracts the venue worker to lead them away. The confrontation heats up and blatant insults are being thrown around. But before it escalates Narcissa arrives and intervenes to avoid drama without realizing that Draco was the instigator. Harry knows discretion is the better part of valor and lets it go acting with grace which internally Narcissa notices but doesn't comment.
Narcissa drags Draco away and calls him out for his bullshit when they aren't at the center of attention. She gets real hacked off when he tries to argue back and she just claps back with “even if he started it think about the time and place Draco Lucius Malfoy” (ie. his stupidity of doing so in a public forum against Harry Potter given Lucius history).
Meanwhile Harry and co. have made their way up the stairs, leading the way up is Arthur and the rest of the Weasley's with Ron, Hermione, and Harry at the end. It's essentially single file up as the left hand side is meant for venue personnel. The situation gets awkward when Draco and Narcissa find Harry at the end of the line up to the box seats. Knowing her son and she puts herself between Draco and Harry. The progression up is slow and obviously is being held up because wizards decided it's best to check for tickets at the top of the stairs instead of at the bottom.
When they are about fifty people from the entrance a conflagration explodes out of the VIP box. This causes a wave of excitement and people begin to press to get a view. It becomes clear something is wrong when a proper explosion happens and real panic sets in when a skull and snake appear in the sky above the VIP box. The panicked energy hits a cresendo when some box seats start tipping into the stadium and start knocking down other support pillars on their way down. Harry is now in alert and ready, but is stuck pressed against the back of Narcissa Malfoy as the crowd is essentially crushing everyone to get down. Then the VIP box which had their seats starts tipping forward and the staircase starts to go with it. Bill reacts quickly and severs the stairs from the box, but this also causes the stairs to snap back violently. Arthur makes a snap decision, barks orders to his elder sons, and tells everyone to grab someone and begins to coordinate a side-along everyone to the tent with Bill, the Twins, and Percy.
At that moment the bottom half of the stairs also begin to have an issue and falls away. Instinctually Harry releases his hold on Hermione's hand and wraps his arms around Narcissa who is holding Draco. The look on Draco's face seeing Harry saving his mother and him is one of horror and surprise. Draco however is pulled away by people try to cling on to people stop themselves from falling. Narcissa frantically tries to think of a spell to save her son from the fall and freezes with fear. Harry jolts her out of her stupor when he grabs her wand and casting impedia and softens the ground saving dozens including Draco. Seconds after Hermione and co disappear via apparation and the sudden loss of force causes Harry to fall backwards which jostles Narcissa's wand loose and it falls and lands on the last step of the section of the stairs. A minute later anti-apparition wards go up and Harry finds himself hugging Narcissa staring at the at sky while panic sets the world below aflame. (Had the idea of Barty Jr being a touch more broken and preferring to take out the traitor Lucius than meeting back up with whatever baby Voldemort was.)