Can this be the antecedent?

Question

Ron snapped. Before Malfoy knew what was happening, Ron was on top of him, wrestling him to the ground. Neville hesitated, then clambered over the back of his seat to help.
"Come on, Harry!" Hermione screamed, leaping onto her seat to watch as Harry sped straight at Snape –– she didn't even notice Malfoy and Ron rolling around under her seat, or the scuffles and yelps coming from the whirl of fists that was Neville, Crabbe, and Goyle.

(Harry Potter and the Sorcerer's Stone)

I’ve read several times this book, yet it’s not easy to understand the bold-faced part whenever I read it. The antecedent, the whirl of fists, doesn’t seem to be equal with Neville, Crabbe, and Goyle. Is this a unique expression of the writer or common in English?

Answer 1

the X that/which is Y, in which X is a metaphor and Y names its referent, is a fairly common rhetorical device in literature and some fancy academic writing. Here are a couple of quick examples from Google:

Only by understanding them can the propagandist control that vast, loose-jointed mechanism which is modern society.
We walk through the kingdom of surprises which is our daily round.
... the complex system that was the medieval cathedral.

This has the form of a restrictive relative clause, but it isn't, really; note that in your example and mine the clause can be omitted without altering the sense of the sentence. It is rather a form of "gloss" which provides the author an unobtrusive way of introducing a vivid image or characterization which might leave the reader scratching his head if it isn't explained.

It may help you parse it if you think of it like this:

... the scuffles and yelps coming from the "whirl of fists" (i.e., Neville, Crabbe, and Goyle).

Answer 2

It's poetic speech, a metaphor. Obviously Neville, Crabbe, and Goyle are not literally "a whirl of fists", I presume they are three boys. (Are they boys? Sorry, haven't read the book.) But the writer is trying to convey the idea that when he looked at the three, rather than seeing three human beings all he saw was a whirl of fists.

A teacher I had many years ago once said, "Every metaphor is a lie, but it contains truth." That's the point of a metaphor. It is not literally true, but it expresses an idea that reflects the truth.