After the incident with the pixies, Lockhart reverts to role-playing in his Dark Arts class. Hermione approaches Lockhart at the end of class and asks for permission to get a book out of the restricted section of the library, in order to better understand the tactics employed in one of his books. Lockhart is very flattered by this attention paid to his works, so he signs the slip, and Harry, Hermione, and Ron hurry into the library, where they are given the book. They read about the painful and complicated steps to making and using Polyjuice potion, and by the end Hermione is the only one still interested in trying to make it, although she persuades the boys to join her.
The Quidditch match between Gryffindor and Slytherin dawns, and during the Gryffindor team pep talk, Oliver Wood reassures his team that while the Slytherins have better brooms, the Gryffindors have better people on their brooms. He then tells Harry to get the Snitch or die trying. The game begins, and as soon as Harry is circling through the air looking for the Snitch, a Bludger streaks toward him, and continues to aim for him, even after knocked away by Fred and George. While the two beaters are protecting Harry, the Slytherins are scoring goal after goal, and during the time-out talk, Harry requests that Fred and George return to the game, allowing him to fend against the Rogue Bludger for himself while he looks for the Snitch. Malfoy, the Slytherin seeker, laughs at Harry for his twirling evasions of the Bludger, and while he is laughing, Harry notices the Snitch next to his face. Harry pauses, is whacked by the Bludger, recovers quickly and flies at Malfoy, grabbing the Snitch and falling out of the sky.
Harry wins the game but lands painfully, and he is greeted on the ground by Lockhart, who immediately sets to repair his broken arm but makes a mistake and de-bones it. Harry is sent to the hospital wing where he must stay the night, waiting for his arm to re-grow itself through a lengthy and painful process. During the night, he is visited by Dobby, who explains that he had closed up the train platform and bewitched the Bludger, both in hopes that Harry would give up and return home and away from Hogwarts, where his life would be threatened because the Chamber of Secrets had been opened again. Harry perks up at this knowledge, wanting to know more from Dobby, but the house-elf is adamant about saying nothing more, and soon footsteps sound in the corridor and Dobby disappears. Dumbledore enters with Professor McGonagall, together carrying a stony figure that Harry soon recognizes as Colin Creevey, who has been petrified with his camera in front of his face. Dumbledore gravely reiterates what Dobby had said, that the Chamber of Secrets has been opened again.
This chapter illustrates the uselessness of Lockhart as a teacher, both when he de-bones Harry's arms instead of fixing it, and when he is flattered and manipulated by Hermione in her mission to obtain the restricted library book. Oddly enough, in this situation Hermione is the one persuading Ron and Harry to break school rules, instead of the other way around. Harry is not the instigator of the detective-work, as he usually is. He is hesitant to get involved in this situation; even though he wants the Heir to be caught, he does not necessarily want to take this potion with all of its risks, in order to determine whether Malfoy is the heir. Perhaps this is because Hermione is Muggle-born and frightened for her own well-being, but most likely it is because she feels competent to solve this mystery, and the author wants to show a situation in which Harry is not the main seeker of some Hogwarts truth. He is brave enough to enter dire situations, and he is loved deeply by people who help him along the way, but in this situation, it should be known that Harry is not the main person "looking" for adventure and trouble.
During the Quidditch game, we see a perfect metaphor for the good of Harry and Gryffindor versus the evil of Malfoy and Slytherin. As Oliver Wood notes, the Slytherins can afford faster broomsticks, but the Gryffindor have trained more and harder on theirs. When the seekers are facing off to find the Snitch, it is telling that Malfoy has the treasured Snitch dangling inches away from his face, but does not notice it because he is so busy ridiculing Harry. Harry, on the other hand, notices his goal immediately, and does not allow a blow from a Bludger to prevent him from flying for the Snitch with all his energy and determination. Malfoy is a character who has options and treasures laid out before him, but is so preoccupied with gloating about them that he never stops to use them properly. Harry, on the other hand, has very little, but is alert and determined and willing to make a full effort, and so he succeeds in this game instead of Malfoy.
Dobby's visit explains many mysteries that until this point had puzzled Harry, and it reiterates the importance of Harry's life to the magical community, as well as hinting further that Harry is more involved, more threatened, by the events at Hogwarts than he could possibly know or understand. Hearing the fear in Dumbledore's voice as Colin is brought to the hospital wing furthers this ominous sentiment; even the world's greatest wizard, and the Hogwarts headmaster, cannot fully understand how these events have come about.
The rogue bludger doesn't cause Harry to lose the bones in his arm, Lockhart does
All the adventures Lockhart writes about did happen, they just didn't happen to him! So this question could be confusing