"Can you hold him still, Harry?"
-- Colin Creevey
Harry begins Quidditch practice, words are exchanged with the Slytherin team, Ron’s spell backfires, Harry and Ron serve detention, and Harry hears a voice.
Calendar and Dates
The entire action of the chapter takes place during a single day, the first Saturday of the Y12 - Y13 school year.
Interesting facts and notes
This chapter marks the first incident in which the epithet "Mudblood" is used, the first appearance of Draco Malfoy in the role of Seeker for Slytherin, and the first time Harry hears the voice of the monster of Slytherin.
He had been unconscious in the hospital wing for the final match of the previous year, meaning that Gryffindor had been a player short and had suffered their worst defeat in three hundred years.
So a team must play with one less player if someone is injured? This is seems absurd and there are several other instances in the books where replacement players are fielded. In fact, Alicia Spinnet was a reserve player the year before she became one of the three Chasers for the team. Did Oliver Wood really not have anyone in reserve, even someone he could have called up at the last moment to fill the spot? What about McClaggen, for example? He'd be a second year at this point.
Several people in green robes were walking onto the field, broomsticks in their hands.
The number is refined a few paragraphs later to clarify that these are just the seven wizards on the Slytherin Quidditch team, who from the description are wearing their Quidditch robes; no other Slytherins are present. Apparently Slytherin, like Gryffindor, is not investing much effort in training reserve players this year.
"Flint!" Wood bellowed at the Slytherin Captain. "This is our practice time! We got up specially!"
On the other hand, if Oliver took as long on the second and third animated diagrams on the first, the Gryffindors wasted the first hour of their practice time sitting through Wood's lecture about their new training program (given their sleepiness, one can't say that the players were actually listening).
Angelina, Alicia, and Katie had come over too. There were no girls on the Slytherin team, who stood shoulder to shoulder, facing the Gryffindors, leering to a man.
This is a detail that the films got wrong; there are no girls on the Slytherin team. Note that the Slytherins are being offensive to the female Gryffindor players.
And from behind the six large figures before them came a seventh, smaller boy, smirking all over his pale, pointed face. It was Draco Malfoy.
We can attempt to work out some of the names of the other six players present by putting together this chapter's information with the Gryffindor/Slytherin matches of PS11,CS10 and PA. (Incidentally, Draco is replacing Terrence Higgs as Seeker.)
One of the six, of course, is the Slytherin captain, Marcus Flint, named in this chapter (who plays Chaser).
Since Adrian Pucey, who plays Chaser, was on the team in PS11 and is mentioned during the play-by-play of Gryffindor versus Slytherin only a few weeks later, it seems reasonable to suppose that he is one of the five unnamed players, leaving the Keeper, the two Beaters, and one more Chaser to be identified.
The Keeper during the previous year was Bletchley, and as Miles Bletchley is the Slytherin Keeper three years later in OP, for simplicity's sake we shall assume that the Bletchley of OP is the same as that of PS, and that he also played the position in CS.
The Slytherin Beaters aren't named in CS, but during the Y13 - Y14 year they will be two sixth-years, Derrick and Bole, so it's possible that they are already Beaters for Slytherin. On the other hand, during the Quidditch final during the Y13 - Y14 year Lee Jordan mentioned that there had been changes in Slytherin's lineup, and the Beaters could've been the subject of that remark.
That leaves us with one Chaser unaccounted for. This could be either Warrington (who will be captain three years from now) or Montague.
"Very latest model. Only came out last month."
That is, the Nimbus Two Thousand and One first came out in August of Y12.
"Givin' me advice on gettin' kelpies out of a well," growled Hagrid, moving a half-plucked rooster off his scrubbed table and setting down the teapot. "Like I don't know."
Hagrid, being expert enough at Care of Magical Creatures to handle hippogriffs, naturally isn't flattered at being instructed in the removal of kelpies; the information can be found under the kelpie entry in (FB, which is a required first-year textbook. Kelpies have a dangerous rating, so it may not be easy to actually do the job, but the information should be common knowledge in the British wizarding world.
At the same time, we're being shown that Hogwarts has roosters on the premises. They'll be mentioned again after the attack on Justin Finch-Fletchley and Nearly-Headless Nick.
"An' bangin' on about some banshee he banished."
Putting this together with Lockhart's list of published works and with his first D.A.D.A lecture in CS6, this would be the Bandon Banshee, the subject of Break with a Banshee.
"He was the on'y man for the job...an' I mean the on'y one. Gettin' very difficult ter find anyone fer the Dark Arts job. People aren't too keen ter take it on, see. They're startin' ter think it's jinxed. No one's lasted long fer a while now."
Which, of course, made it much easier for Dumbledore to hire Remus Lupin the following year, so this isn't entirely a bad thing. On the other hand, it's also why the job was open three years later for Dolores Umbridge...
"Fourteen times he made me buff up that Quidditch cup before he was satisfied."
Why isn't the Quidditch Cup in Snape's study, since his House won it the previous year? From McGonagall's remarks in OP, the Head of House for the House that wins the Quidditch cup has possession of the cup for the following year.
"And then I had another slug attack all over a Special Award for Services to the school."
Riddle's award for catching the monster of Slytherin, of course, as we shall see later.
Exceptional character moments
Oliver Wood's fanaticism, going through three animated diagrams - at twenty minutes apiece - at dawn on a Saturday morning to a sleep-deprived audience.
Ron, pulling a wand and attempting to curse Draco Malfoy for insulting Hermione.
The twins, attempting to pound Malfoy for insulting Hermione.
Ron, offering to swap detentions with Harry to avoid Filch and "Muggle cleaning" in the trophy room.
Harry, offering to swap detentions with Ron to avoid Lockhart.
McGonagall, for having assigned those detentions in the first place.
Hagrid, teasing Harry about the signed photos and about Ginny hanging around.
Harry didn't know how to get rid of him. It was like having an extremely talkative shadow.