Photo: Ezra Shaw / Getty Images Photo: Ezra Shaw / Getty Images Photo: Scott Strazzante / The Chronicle Photo: MediaNews Group/The Mercury News Via Getty Images / MediaNews Group Via Getty Images Photo: Rich Pedroncelli / Associated Press Photo: Scott Strazzante / The Chronicle Photo: Jeff Chiu / Associated Press Photo: Jeff Chiu / Associated Press Photo: Courtesy Anthony Poole Photo: Scott Strazzante / The Chronicle Photo: Santiago Mejia / The Chronicle Photo: Brandon Dill, Associated Press Photo: Scott Strazzante / The Chronicle Photo: Scott Strazzante / The Chronicle Photo: Scott Strazzante / The Chronicle Photo: Stephen Lam / Special To The Chronicle Photo: Daniel Shirey / Getty Images

Barely one month into his rookie season, Warriors guard Jordan Poole finds himself in uncharted territory.

He has endured shooting slumps before, but nothing as deep and suffocating as this one. Not on this stage. Not to this extreme. Not to the point that Draymond Green animatedly lectures him during a timeout huddle, in full public view.

Poole’s defining trait has been his good-natured swagger, an unwavering self-confidence in his basketball ability. This traces to long-ago pickup games in his hometown of Milwaukee, when a young Poole played against adults, and extends through his high school career and two years at the University of Michigan.

And now, as a first-round draft choice prematurely thrust into a prominent role for a high-profile NBA team, Poole’s confidence is absorbing a vigorous test. He keeps shooting, of course, but the ball keeps clanging off the rim, rudely and relentlessly.

Poole shot 2-for-13 from the field in the season opener Oct. 24, launching a parade of ugly numbers: 3-for-16 against the Blazers, 2-for-11 against the Rockets, 1-for-8 against the Celtics, 0-for-7 against the Pelicans (the game in which Green gave him an earful). Poole is shooting 26.8% from the field, including 24.5% from 3-point range. He has made at least half his shots in one game all season (7-for-13 against the Spurs on Nov. 1).

So now the question becomes: Can he draw on his past to escape this rut?

Jim Gosz knows all about Poole’s overdose of swag.

Gosz, one of the most accomplished high school basketball coaches in Wisconsin, saw it in Poole’s perpetual little smirk. And in the way he rolled up his pants, or left the strings dangling out of his shorts.

Long before he reached the NBA — and instantly collected significant playing time, given Klay Thompson’s torn ACL and then Stephen Curry’s broken hand — Poole exuded a distinctive blend of bravado and playfulness.

“That swag has carried him,” Gosz said. “That’s his MO. He’s backed it up everywhere he’s gone. I’m sure at times his teammates want to choke him, but he’s a good team player and he can take coaching.”

This matters for the Warriors, who need Poole, a 6-foot-5 shooting guard, to develop for the long-term. They took him with the No. 28 overall pick in this year’s draft, one day after Poole turned 20. He’s more than 2½ years younger than second-round selection Eric Paschall, who celebrated his 23rd birthday this month — and already has established himself as one of the league’s top rookies.

Photo: Courtesy Anthony Poole

Gosz met Poole when he was an eighth-grader and looked like a fourth-grader (as Gosz put it), skinny with no hint of facial hair. Then, as a freshman at Rufus King High, Poole made varsity even though he stood only 6 feet, wasn’t especially quick and barely touched the net with a running start.

But Poole could shoot — boy, could he shoot — and he was not the least bit intimidated. King trailed by three points with eight seconds left in a sectional playoff game during Poole’s freshman year, when Gosz peered down the bench and saw Poole staring back with those “puppy eyes.” He hadn’t played much in the game, but Gosz sent him in.

Poole promptly drained a 3-point shot to tie the score. King won in overtime to advance to the state tournament.

“He’s just a resilient kid,” Gosz said, “and he has no conscience.”

This helps explain why Poole’s college coach, John Beilein (then of Michigan, now with the Cleveland Cavaliers), once described him as having an “overdose of swag.” That label followed Poole, if only because it succinctly captured his free spirit and boundless faith in himself.

Any search for the roots of his swagger inevitably lead to long-ago pickup games at an elementary-school gym in Milwaukee. His dad, Anthony Poole — who grew up on the rugged South Side of Chicago and played football at Wisconsin-Whitewater — ran open gyms at 6 p.m. Sundays while Jordan was growing up.

The games were full of former Division I college players, many of whom played professionally overseas. Jordan Poole tagged along and watched, until about age 12. Then he persuaded his dad to let him play.

Poole's game-by-game stats Date Opponent FGM-FGA Points Oct. 24 Clippers 2-13 5 Oct. 27 Thunder 1-9 6 Oct. 28 Pelicans 4-10 13 Oct. 30 Suns 2-8 9 Nov. 1 Spurs 7-13 20 Nov. 2 Hornets 2-9 5 Nov. 4 Blazers 3-16 16 Nov. 6 Rockets 2-11 8 Nov. 8 Timberwolves 3-10 9 Nov. 9 Thunder 2-6 4 Nov. 11 Jazz 5-11 11 Nov. 13 Lakers 4-15 11 Nov. 15 Celtics 1-8 4 Nov. 17 Pelicans 0-7 0 Nov. 19 Grizzlies 2-8 5 Nov. 20 Mavericks 5-14 11 Nov. 22 Jazz 4-13 13 Nov. 25 Thunder 3-13 11

“I would play with grown men all the time,” Poole said. “Nothing was really given to me; they made me work for it. I was physically not on the same level as they were, so I had to find ways to score. That kind of made me tough.”

One time, when Jordan was in eighth or ninth grade, he went in for a layup and had it emphatically blocked. Deonte Burton, who is 2½ years older and now plays for the Oklahoma City Thunder, punctuated the block with some lively words for the youngster.

The next time downcourt, Poole lofted his shot a bit higher and scored on Burton — and chirped right back at him.

“It was real basketball,” Anthony Poole said of those pickup games. “They were rough on him, and there was some trash talking and pushing. Sometimes, guys got mad at Jordan because he was talking crap to them, too.”

Poole found a worthy partner in swagger when he arrived in the Bay Area this past summer. One complicating factor: Green is a proud Michigan State alum and Poole spent his two college seasons at State’s biggest rival.

Poole had the locker next to Green’s at the team’s old practice facility in downtown Oakland over the summer. One day in July, Poole left his blue Michigan duffel bag between their spots — and returned to find it flung across the room, its contents scattered on the floor.

Now he knows better than to leave any Wolverines gear within sight of a certain Spartan.

“His rookie year will be tough if he wears Michigan stuff,” Green said, not really smiling.

Photo: Charlie Riedel / Associated Press

But the opening volley didn’t diminish a budding connection. Green requested that he and Poole remain neighbors in their new Chase Center locker room, allowing more time for mentoring.

Green sees potential in Poole, and not merely because of his smooth shooting stroke (worth noting: he’s shooting 89% from the free-throw line). Poole stood up to Green during one training-camp scrimmage, matching his volume despite their disparity in experience.

Then, in his first exhibition game, Poole tangled with Lakers forward Anthony Davis, kind of pushing him over. Davis defiantly hopped off the court and teammate Avery Bradley quickly joined in, seeking to put Poole in his place.

He firmly stood his ground, much to Green’s satisfaction.

“He’s not going to back down from anybody,” Green said. “I love that.”

As for his exchange with Green in camp, Poole said, “For some reason, rookies aren’t supposed to talk that much. I’m competitive. Just because Draymond is a three-time All-Star, that doesn’t mean I’m not going to talk to you.”

This feistiness showed again Nov. 4, during a rare Warriors win over Portland. Poole, despite his shooting struggles, wowed the crowd with a flashy crossover dribble and step-back 3-pointer over Damian Lillard. Poole animatedly exulted, and yapped, all the way back downcourt.

Later in the game, he agitated forward Rodney Hood to the point Hood blatantly shoved Poole to the floor. The refs didn’t see that, but they handed Poole a technical for his response.

All this chatter requires performance, ultimately, and Poole is not producing right now — though he has scored at least 11 points in each of the Warriors’ past three games. Widen the scope, and it’s still too early to tell if he will pan out for the long haul.

Gosz candidly called him a defensive liability in high school, and Poole’s shot selection, strength and defense clearly need to improve for him to last in the NBA. He’s not especially athletic, a big problem at a position filled with elite athletes.

Also, let’s face it: The Warriors drafted Poole mostly for his shooting, which makes his miserable start all the more troubling. Gosz saw him swish 16 consecutive 3-point tries in warm-ups before Michigan played Wisconsin last season, and he holds his own in post-practice shooting contests with Thompson and D’Angelo Russell.

Poole might learn a thing or two competing against those two players (and Curry) from beyond the arc.

Along the way, he will stay free-spirited. Anthony Poole recalled the way Jordan occasionally hung out with unpopular kids in high school, just because he felt like it. Or wore skin-tight jeans when none of his peers did.

“Jordan has always been comfortable in his own skin and rocked to his own beat,” Anthony Poole said.

And now, more than ever, he needs to rediscover his rhythm.

Ron Kroichick is a San Francisco Chronicle staff writer. Email: rkroichick@sfchronicle.com Twitter: @ronkroichick