Colin Kaepernick’s playful smile faded as each pass whistled past its target. The 49ers quarterback was attempting to be the first to swish a football into a butterfly net in the right corner of the end zone during a training-camp drill.

It is, of course, that nightmarish sector of the field where the 49ers’ past two seasons have ended on throws by Kaepernick. Three incomplete passes headed for Michael Crabtree in the waning moments of Super Bowl XLVII in New Orleans. And in the final moment of last season, another throw to Crabtree in the right corner was tipped by Richard Sherman for an interception that sealed the NFC Championship loss against bitter rival Seattle.

It is enough to make Kaepernick’s steely focus even more intense. And enough for league experts to wonder if Kaepernick is the guy who can lead the 49ers to their first Super Bowl title in 20 years.

He is the NFL’s most cutting-edge quarterback — and also one of its most polarizing.

“There were people, from the time he took over for Alex Smith, that were looking for him to fail and wondering when that’s going to be,” said John Madden, the Hall of Fame former coach and broadcaster. “I look and don’t think it ever is going to be.”

The doubts about Kaepernick’s potential to become one of the NFL’s elite quarterbacks seem to be dissipating. His passing stats might not impress people, but his work ethic and competitive fire do. He hasn’t seized the big moment yet, but all the big-moment experience he has stored in less than two full seasons scares the heck out of defensive coordinators.

“People don’t talk enough about how the guy is an absolute competitor and battler,” one such coordinator shared on the condition of anonymity. “This guy’s a bad ass. This guy’s going to battle you to the end.”

When it was all over in Seattle last January, Kaepernick already was one step ahead of his critics.

“I didn’t play good enough to win,” he said. “I turned the ball over three times. I cost us that game.”

Some won’t be convinced Kaepernick, 26, is trustworthy as a clutch performer until those final chapters have different endings.

Sports Illustrated’s Peter King wrote in his pre-camp rankings that if he trusted Kaepernick as much as Seattle’s Russell Wilson, the 49ers would have been his No. 1 team and the Seahawks No. 3, instead of vice versa.

“If you talk to someone with a pure-passing pedigree, they won’t trust Kap yet,” said Trent Dilfer, an ESPN analyst and former 49ers quarterback. “If you talk to a new-school guy that likes dynamic athletes that outweigh traditional passers, he’ll trust him.”

“His teammates trust him,” said Bill Polian, an ESPN analyst and former Indianapolis Colts president. “Who cares if the nation trusts him? He’s not running for office.”

There is plenty for his teammates and coaches to believe in. Kaepernick’s face is routinely the first they see upon arrival at their Santa Clara facility in the morning and the last they see when leaving at night. And he is fresh off signing a team-friendly six-year contract extension where his value (potentially $126 million) is tied to the 49ers’ success, per his request.

“The thing about Colin is he’s not afraid to work. He’s a bulldog,” 49ers general manager Trent Baalke said.

More is expected from a passing attack that ranked 30th last season, and Kaepernick has prepared himself to take advantage of a deeper receiving corps and to capitalize when the stakes are raised.

“Lately we’ve worked on a lot of red-zone throws,” wide receiver Anquan Boldin said. “That’s something we put emphasis on.”

Kaepernick also is embracing his role as a vocal leader. After young tailback Jewel Hampton got into a minor scuffle in camp, Kaepernick pulled him aside for counsel. When linebacker Aldon Smith emerged from a dominating drill, Kaepernick was there to exchange a subtle high-five.

“Sometimes he’ll speak up in meetings and give his expectations for landmarks and locations of the ball,” wide receiver Brandon Lloyd said. “He’ll have the floor in the meeting and he’ll discuss what he sees and what he expects out of the plays.”

Kaepernick’s love of “Kaepernicking,” where he kisses the biblical tattoos on his right biceps after a touchdown run, has led some outsiders to question whether he is more me-first than team-first. But look closely when his teammates find the end zone and you’ll see a smiling Kaepernick in full sprint to congratulate them.

Kaepernick recently acknowledged that he believes stereotypes dictate the way he is perceived.

“Between the tattoos, the way I dress, the way I talk, people don’t think it should go together with being a franchise quarterback or somebody leading a team or representing the organization,” he told Bleacher Report.

Yet long before “Kaepernicking” was a thing and people wondered if he was spending too much time savoring his newfound celebrity at award shows and on magazine covers, there were critics. They wondered if the second-round draft pick out of Nevada could move from a pistol offense to a West Coast system. If his windup throwing motion needed an overhaul. If he would rely too much on his long, speedy legs.

As Kaepernick started slowly last season — one 200-yard passing game from Week 2 to 11 — the line of questioning centered on whether he could go through progressions and read defenses. Dilfer drew Kaepernick’s ire for his pointed criticism, but now is quick to note how the young quarterback has improved.

“He’s really worked hard on (progressions) and you can tell,” Dilfer said. “We talked at the Super Bowl. … Kap has a burning desire to be great. That’s a big deal.”

Polian said Kaepernick improved late last season, citing his secondary reads and passing to underneath receivers.

“He’s going to get better simply by having more opportunities to learn defenses and how to manipulate them,” Polian said.

For perspective, consider Kaepernick’s 639 career regular-season passes. That ranks 45th among quarterbacks in this summer’s training camps. Leading the way are Peyton Manning (8,452), Drew Brees (6,799) and Tom Brady (6,586). Even Seattle’s Wilson has more attempts (800) dating to his 2012 rookie season.

Only Philadelphia’s Nick Foles got more out of his completions than Kaepernick last season, according to FootballPerspective.com, which used statistical analysis factoring in yards-per-completion, the league average and attempts.

And Kaepernick tied for the fifth-best accuracy percentage last season on passes of 20 yards or longer, according to ProFootballFocus.com.

An offseason that brought in veteran receivers Steve Johnson and Lloyd, as well as rookie Bruce Ellington, is bound to open up the 49ers’ passing game. Boldin re-signed rather than hit free agency, Crabtree has looked hungry entering his final season under contract, and tight end Vernon Davis (13 touchdown catches in 2013) opted to cut short his contract holdout.

“When he gets all the parts and gets his receivers going, he’ll be fine,” Madden said.

Expectations were tempered early last season while Crabtree missed the first 11 games recovering from Achilles surgery. Kaepernick’s completion percentage slipped from 62.4 in 2012 to 58.4. Even after Crabtree returned, that percentage dipped to 54.9 in three playoff games.

But, Madden pointed out: “He’s not going to be one of the guys with a high percentage, because he’s going to take more chances.”

Dilfer agreed, adding: “Kap’s not in a system where he’s going to throw 65 to 68 percent. It’s a run-first offense, where they set up the big play off the run. He’s very accurate down the field. He’ll become more efficient when he sees more looks and then will make better decisions.”

There were plenty who questioned Kaepernick’s off-field decision-making in the offseason after he was named in a Miami police investigation in April. The incident was initially referred to as a “sexual-assault case” by TMZ.com and other media outlets, even though no crime or sexual action was alleged and no charges were filed.

“As I said from Day 1, I would never do the things that were made up about me,” Kaepernick said via Twitter. ” I’m glad this issue is resolved. It’s time for football.”

Kaepernick had been in Miami to work out before the 49ers’ offseason program. Boldin and wide receiver Quinton Patton took part in those sessions, not just to break a sweat, but to help Kaepernick refine his timing on passes.

“He has a big-time arm that, on quick-in throws, he can get the ball to featured guys pretty easily,” said the defensive coordinator who wished to remain anonymous. The coordinator also downplayed Kaepernick’s progression-reading woes.

Roger Theder, a former Cal coach who tutored Kaepernick in his Pitman High-Turlock days before the 49ers drafted him in 2011, likes what he sees from his former pupil, both technically and mentally.

“Colin stands tall, has a narrow base, throws really well, turns his shoulder really well,” Theder said. “And he’s got that great work ethic.”

To make play calls easier and cut down on play-clock woes, the 49ers simplified this season’s playbook, so much so that coach Jim Harbaugh described Kaepernick’s expertise as “auto-correct” mode.

This is the job Kaepernick craved since he was a kid helping the Turlock Vikings win trophies as a quarterback and safety. He has been a relentless competitor ever since, said his father, Rick, who linked that trait to a motivational poster that hung next to his bed.

“The power to win must come from within,” read the poster, featuring a player trying to break a tackle to dive for the goal line.

Asked about it after a 49ers practice, Kaepernick said the poster “was just another reminder that if you’re going to do something, the biggest factor is you. ‘How much do you want it? How much work are you willing to put in to accomplish it?’ … It made it that much easier to wake up and say, ‘OK, if I want this, I’m going to go after it.’ “

Those words came shortly after an extra workout on an otherwise deserted practice field. A couple hours earlier, he had been practicing with his fellow quarterbacks. Of course it was Kaepernick who first nailed a fade pass into that butterfly net.

“I look at guys and ask how would I like to coach against them,” Madden said. “He’d be a pain in the butt. He has the arm, athletic ability, he can move in the pocket, he can run with the ball, he can run fast with the ball.

“I think he’s great, not just with the things he does, but what he is capable of doing.”

For more on the 49ers, see Cam Inman’s Hot Read blog at blogs.mercurynews.com/49ers. Follow him on Twitter at twitter.com/CamInman.