Here's the breakdown:
* Draco Malfoy, a Slytherin student who has a deep rivalry with Harry, used a jinx to cause the broom to malfunction.
* Professor McGonagall was initially suspicious, but couldn't prove it was Draco.
* Hermione Granger figured out the truth when she noticed Draco muttering under his breath and remembered a jinx she had learned about from a book.
* Albus Dumbledore intervened, using his magic to counteract the jinx, and saved Harry from falling.
This incident highlights the magical rivalry between Harry and Draco, as well as the power and dangers of dark magic.