The Secret History of the Golden State Warriors' Unstoppable Play

“That was something I drew up a long, long time ago,” said Stew Morrill.

The clever play that Morrill doodled on a chalkboard in the Montana coach’s office more than 30 years ago soon began to spread, and it was such a good idea that it was adopted by rival coaches and local high schools wherever Morrill coached.

But how did something drawn up a long, long time ago eventually make its way to the Warriors? It took an unlikely series of seemingly unrelated heists for this one play to be perfected by one of the best teams in the history of basketball. And not even the people involved fully understood their pivotal roles in the chain that links Morrill to a potential NBA dynasty.

One summer day in 2015, Steve Kerr was having lunch with Fred Hoiberg. Kerr had recently coached Golden State to a championship, and Hoiberg had recently left his college job for the Chicago Bulls. They were chatting about basketball strategy when Hoiberg said he’d noticed that the Warriors used one of his plays. Kerr told him they actually named it Cyclone in honor of Iowa State.

That’s when Hoiberg confessed. It wasn’t his play. He’d taken it from BYU coach Dave Rose. And it wasn’t his play, either. “We’re all thieves in this business,” Hoiberg said.

But someone at some point had to come up with something original. As it turns out, when you trace the play back to its origins, that someone was Stew Morrill.

Morrill, who retired in 2015 after more than 600 wins at three schools, had a reputation among his peers for this sort of X’s and O’s wizardry. “I love Stew’s stuff,” Hoiberg said. Morrill was a widely respected tactician. There was nothing he enjoyed more than being in his office late at night eating pizza, drinking beer and diagraming plays.

“Sometimes it was really good, and sometimes it was really bad,” Morrill said. “Dribble was one of those that was really good.”

He came up with Dribble all the way back in 1986, his first season as a head coach, while tinkering with his trusty assistant Blaine Taylor. It had everything they wanted in a set play. It was quick. It was deceptive. And it was almost impossible to defend when executed properly.

Here’s how it works. The play begins with the misdirection of two guards whooshing past each other underneath the basket. One guard (Andre Iguodala below) continues to the wing and catches the first pass as the other guard (Stephen Curry) curls upward and sets a back-screen for a big man (Draymond Green). “There is no play if the guy doesn’t set a bone-crusher,” Morrill said. Then comes a pass from Iguodala to Green rolling off the Curry pick. If everything goes to plan—the cross, the first pass, the screen and the second precisely timed pass—the finish should be the easiest part.

Morrill’s teams ran this play so many times in so many games for so many layups that eventually they had to get creative with it. He disguised his calls using an elaborate system of cards—“we weren’t yelling Dribble,” he said—and took his precautionary measures to the extreme in league games against the opponents they played every year.

“We saved it for the second half when the offense was in front of our bench,” Morrill said, “so the other coaches couldn’t call it out.”

But even calling it out isn’t always enough. NBA coaches know that Cyclone is one of the Warriors’ favorite plays. In the fourth quarter of a tight game last year, Detroit coach Stan Van Gundy sniffed it out immediately and pointed out exactly what was about to happen: the Curry back-screen, the Klay Thompson pass, the Green dunk. It happened anyway.

There is a paradox at the heart of Morrill’s play: It turns a shooter into a screener. The play is devastating for the Warriors because Curry becomes a decoy. The only way to disrupt Cyclone is for the defenders to switch when they realize they’re in the eye of the storm. But the problem is that every basketball player on the planet’s instinct is to stick with Curry, and his gravity creates a brief opening for Green to sneak toward the basket after the back-screen for a shot even more valuable than a Curry three.

“If you have a good shooter setting that screen, you get layups,” Hoiberg said.

And if you have the greatest shooter ever?

“I’ll say this,” he said. “It’s really good when Steph Curry sets it.”

The Warriors aren’t known for running set plays. Their offense is a blur of cuts and constant motion as blissful to watch as it is brutal to stop. This one is so unusual, and so obviously successful, that it has become a source of curiosity itself.

The blog Golden State of Mind published an explainer about the play in November and said it was called Cyclone because of the way “players end up going in a whirling pattern.” That was both right and completely wrong. Kerr, who declined to comment for this article because he prefers not to discuss the details of his team’s plays, revealed on The Bill Simmons Podcast that it was called Cyclone simply because of he took it from Iowa State.

Hoiberg recently asked Bulls assistant Nate Loenser if he could remember any notable examples of the Cyclones running the play they called Cougar. Loenser barely had to think about it. The second half of their Big 12 Tournament game against Kansas in 2014, he said.

Kerr was in television at the time and happened to be assigned Iowa State’s broadcasts in the NCAA tournament less than a week later. It was clear to anyone who listened to his commentary that Kerr was ready to be a coach, and he’d been quietly building a library of cool plays that he liked. “There’s no patent on this stuff,” Taylor said. Every good idea in basketball is up for grabs. The culture of sharing among coaches means the smartest thing you can do if you like another team’s play is to plagiarize it.

Kerr was hired by Golden State not long after his Iowa State calls. The Warriors have been running the cool play he liked ever since.

Kerr wasn’t the only coach who admired Hoiberg’s play. Rose also found himself intrigued—but for another reason. The play looked awfully familiar to him. “I had no idea where he got it,” Rose said.

He got it from Rose. Hoiberg hadn’t bothered telling him that he was so envious of a certain play while scouting BYU before their games in 2012 and 2013 that he swindled it. Which was oddly appropriate. Rose hadn’t bothered telling Morrill that he inherited Dribble when he poached assistant coach Dave Rice from Utah State in 2005.

Rose liked Morrill’s play, Hoiberg liked Rose’s play and Kerr liked Hoiberg’s play enough to bring it to the highest level of basketball. It’s effective in the NBA because of the extra space, and it’s effective for the Warriors because of Curry, but it’s more or less the same Dribble that was getting layups for the Montana Grizzlies.

Morrill takes a deep satisfaction in the way his invention has endured. “There’s Dribble,” he tells his wife when they watch basketball on the couch. It’s more charming now than when he was still coaching and other teams used his own creation against him. Some of them even called it Aggie while playing the Utah State Aggies. There was a time when it was so popular that Morrill went out of his way to warn players: “Don’t get beat on our own play.”

Hoiberg can relate. The Warriors were playing the Bulls earlier this season when they decided it was time. They had to run Cyclone. As soon as the play was over—Golden State got a dunk out of it—Hoiberg looked down the sideline only to find Kerr already looking for him.

They both understood why the Warriors’ coach was cracking up.

Write to Ben Cohen at ben.cohen@wsj.com