"Mudbloods of course. In the dungeons. Your idea wasn't it? What's going on with you?"
-- Polly Chapman (CC3.2)
He then encounters Polly Chapman, who wants him to take her as his date to the Blood Ball. She also mentions the blood from Mudbloods that has got onto her shoes. Scorpius is appalled by what he is hearing and seeing (CC3.2).
Later the same day as the previous event, late September or early October 2020
This event takes place during the Scorpion King timeline, as described in the essay "Albus Potter and the lesson in Quantum Mechanics" by Nick Moline.
The evil being done in the school (torturing of "Mudbloods", targeting of students who don't conform) seems natural in a school being run by Dolores Umbridge - she embraced "nastiness" (CC3.2).
This is also the first time Scorpius Malfoy's nickname of "Scorpion King" is used (CC3.2).
From the Web
Pottermore: Harry Potter and the Cursed Child
The theatre production opened in the West End of London at the Palace Theatre on 30 July 2016, with Anthony Boyle in the role of Scorpius Malfoy, James Le Lacheur as Yann Fredericks, Jack North as Karl Jenkins and Claudia Grant as Polly Chapman: Harry Potter and the Cursed Child, Parts One and Two