At some point in almost every Blackhawks home game, more than 20,000 people will stand, cheer and start singing nonsense.

The drums start and the sound of guitars playing a G-major chord fills the United Center. Then: Ba-da-dut. Ba-dut-do. Ba-da-do-da-do-da-do.

And again. Then comes a D-major chord, and they sing the melody again, only lower, while the players celebrate.

Since 2009 this ritual of singing the chorus to "Chelsea Dagger" after every goal is as ingrained in the experience of a Hawks game as cheering during the national anthem and drinking beer.

The song, by the Scottish band the Fratellis and in which lead singer Jon Fratelli wrote about a burlesque performer, is regarded as one of the best goal songs in the NHL.

But just what is it about the song — its melody, lyrics and arrangement — that makes it such an effective ear worm that you can't get out of your head?

You may not know the rest of the lyrics and you may not know the melody of the verses, but like a lot of pop and rock music, all that matters is the chorus. In the case of "Chelsea Dagger," it employs a few different songwriting motifs to make sure it sticks in your brain, perhaps to the point of annoyance.

"It's sort of the right combination of multiple elements coming together all in the right way," said Chris Sampson, a professor of popular music at USC. "I think if you separate out the elements on a singular basis, it may not add up to that same effect."

It may sound simple, but there's a lot going on in the chorus' few seconds. Sampson said Fratelli used "tried and true" songwriting techniques like repetition and sequencing when concocting the chorus. And Fratelli did something Sampson teaches his songwriting students: Invoke audience participation.

In some songs, that takes the form of a command, such as: "Now, put your hands in the air." In the case of "Chelsea Dagger," the pub-like, drunken feel is the hook for audience participation.

"The melody starts to sort of inform the sonic sounds of those syllables," Sampson said. "So I think in combination with that melody, they're fused together ... they're almost inseparable at that point. A lot of songwriters actually will begin the writing process by singing nonsense syllables while they're crafting a melody. This technique helps because it sort of informs the sonic quality of the language they might use."

What makes a great sports song? To compile this list, we considered several factors: How good the song actually is, how Chicago teams have used the song and the impact the song has made on Chicago sports and sports in general. (Chris Hine) (Chris Hine)

And sometimes those nonsense syllables sound so natural that the writers just leave them. In that way, "Chelsea Dagger" is akin to other songs with only sounds for lyrics in the chorus, like "Da Doo Ron Ron" by the Crystals or Manfred Mann's "Doo Wah Diddy Diddy," both written by the songwriting pair of Jeff Barry and Ellie Greenwich, who wrote multiple pop standards in the 1960s centered around that technique.

Then there's the melody itself, which is rare because it is cramped in a confined space of just a few notes.

"This shape is probably what's so memorable — a tune that goes up and down again and again within a very small range, so that even if you don't remember the notes or you can't decipher the words, you still have a sense of how it goes," John Liberatore, assistant professor of music theory and composition at Notre Dame, said.

If you play the first six notes on a piano, they are D, D-sharp, E and then back down again with a brief jump to G in the second part. When the chord changes halfway through, the notes go down to A, A-sharp, B with a brief jump to D.

It creates a "kind of teeter-totter torque," Karin Hendricks, an assistant professor of music at Boston University, explained.

"The chorus has a relatively small range and is also repetitive, making it both easy to sing and to remember," Hendricks said. "Its short, breathy motifs give the impression of never ending, while at the same time allowing entrance just about anywhere. Like other kinds of traditional community music, this effect allows entrance, exit and participation by anyone at any time."

Sampson said the melody is recognizable for a reason.

"It's sort of ubiquitous in folk music because it's so singable and so predictable it's almost in our American music DNA, our vocabulary," Sampson said. "So really leaning on those particular notes has worked for hundreds of years in invoking that sort of singalong mentality."

The next key component comes in the arrangement and tempo of the song.

The tempo is about 155 beats per minute. Not too fast, not too slow, Sampson said.

"If it's too fast, it gets washed up in that large space. If it's too slow, then the energy gets lost," Sampson said. "This tempo gives it that energy, but at the same time people can lock in with it."

And whereas Fratelli is singing solo with no backup on the verses and pre-chorus sections, he sounds as if he's in a bar on the chorus with plenty of layered and overdubbed vocals on top of his.

"It has a bizarre sense of happiness," said Kurt Westerberg, a professor of composition and musicianship at DePaul. "It's like the Roadrunner beating (Wile E.) Coyote — there's this happy music when somebody is dead. … It gives you the feeling like you're dancing on somebody's grave."

That's what it can feel like in a hockey game after a goal. The enjoyment of hearing the song is still there for Hawks players. Perhaps some of that is positive reinforcement — they hear the song only after something good happens, but it hasn't worn on them yet.

"It gives good memories," former defenseman Brian Campbell said. "That's the thing. Sometimes you go to a bar and you hear it and everybody gets excited about it. Seeing how loud the fans get with that song is the excitement we get out of it."

And thanks to its composition and lyrics — or lack thereof — fans can get as loud as they would like.

chine@chicagotribune.com

Twitter @ChristopherHine