Saturday night the boys at Pencey always get steak for dinner. Primarily, Holden tells us, this is because everyone's parents come to visit on Sunday, and this way, when they ask what their son had for dinner last night, he'll say "steak."
Holden and his friend Mal Brossard take the bus into town for the night. He convinces Mal to let Ackley come along with them (because otherwise the kid will sit in his room and pick his pimples all night).
It's snowing (since it's December in Pennsylvania) and Holden packs a snowball. He tries to throw it at about ten different objects but keeps changing his mind, and finally just carries it around until they get on the bus and the driver tells him to ditch it.
They don't end up going to the movie theater after all, since Mal and Ackley already saw it and Holden doesn't like watching movies with people that laugh at stuff that isn't even funny.
When they get back to the dorm, Ackley sits on Holden's bed and picks his pimples and won't leave after a barrage of hints that, really, he should leave. Ackley then proceeds to tell a fake sex story (and we can tell it's fake because it contains inconsistencies).
Once Ackley leaves, Holden puts on pajamas, a bathrobe, and his red hunting hat to write Stradlater's composition.
It's supposed to be a descriptive work, but Holden can't think of a room or a house or anything like that as he was supposed to write. All he can think of is his brother Allie's baseball mitt.
Allie was left-handed and (accordingly) had a left-handed fielder's mitt. The thing about it is that it was covered in poems that Allie had written on in green ink so that he'd have something to do (that is, read the poems).
Allie's dead now, Holden tells us. He died from leukemia in 1946 (which we can infer to be three years before the events taking place, and four years before Holden's telling us this story). He (Allie) was intelligent and good-natured and had red hair – the kind you could see from a mile away. He used to laugh so hard he'd fall off his chair. Holden then gets to some Pretty Important Stuff: The night that Allie died, he (Holden) went into the garage and broke all the windows with his fist – "just for the hell of it." He tried to break all the windows on the car, too, but his hand was already broken. He still can't make a good fist, but whatever – it's not like he's going to be a violinist or something, he says.
So that's what Holden writes the composition about – the baseball glove. He listens to Ackley snoring and feels "a little sorry for the crazy sonuvabitch."