By Michael Pina

As any NBA player advances through a career, it's nice to believe his professional growth is organic -- an inevitable happening founded on individual work ethic, natural evolution and the in-season progress we've all watched unfold.

The fact is, nobody knows how good a young basketball player will ultimately become, and nobody knows how their skills will progress from one season to the next.

This season a handful of young players have leapt forward in various impressive ways, including Paul George, Anthony Davis, Lance Stephenson, Andre Drummond, Terrence Jones, Jared Sullinger and DeMar DeRozan, just to name a few.

But degrees of improvement aren't the same for everybody, and there are no guarantees anything happens at all (see: Evans, Tyreke). Through the first half of this season, three young, talented players of note have, statistically speaking, failed to show the type of progress that was expected. They are San Antonio Spurs forward Kawhi Leonard, Chicago Bulls guard Jimmy Butler and Golden State Warriors forward Harrison Barnes.

All three have less than three complete seasons under their belt. All three ended the 2012-13 campaign with a "breakout" playoff run. Why haven't they been better? Is it possible they aren't the players we thought they were? Are any in danger of stalling out? Or are there different, encouraging explanations for the stunt in their development?

Kawhi Leonard

Why were expectations for Leonard so high heading into this year? For starters, let's compare his second season with that of Indiana Pacers He-Man Paul George. Leonard was arguably the better player, and he elevated his play to another level in the playoffs, serving as the second best overall player on a team that was an eyelash away from winning the title. He was 21 years old. This remains insane seven months later.

Leonard was a monster on the boards. He appeared to be the only player in the world who could guard LeBron James one-on-one and make him work on the other end. Leonard's versatility in that series was special, and this year we were supposed to see a significant, easily identifiable boost.

George did it with Indiana and is now, in his fourth season, one of the five or six best players in the league. Why isn't Leonard making the same jump?

The simple answer is also boring: The Spurs are too good. Tony Parker is once again having a phenomenal, All-Star worthy season; Manu Ginobili is back to being a legitimate candidate for Sixth Man of the Year; and Tim Duncan is Tim Duncan. Their 32-9 record is best in the Western Conference, and they outscore opponents by 12.4 points per 100 possessions when Leonard sits as opposed to 6.6 when he plays.

Leonard's usage rate (currently lower than Marco Belinelli's) and PER are a hair better than last year, but not quite on George's level. Only three other players in the entire league use less of their team's possessions while matching Leonard's minutes and PER, according to Basketball-Reference. Two of them are DeAndre Jordan and Andre Drummond, behemoths who only operate around the rim, and the third is Anderson Varejao.

Leonard's usage rate is also actually lower than average when Danny Green, who's out another few weeks with a wrist injury, is not on the floor. That's weird. Comparisons between Leonard and George lose steam when you start putting their roles into context. Both play for contenders, but the Spurs have yet to need Leonard to increase his production.

Here are a few statistical categories where he's taken a step back: free-throw rate (career-low .159), three-point percentage (career-low 32.3 percent), points (0.1 lower than last season) and personal fouls per game.

In what may be the weirdest footnote of all, Leonard hasn't been on the court as often, averaging 2.3 fewer minutes per game.

All that said, he's still been a very effective scorer, devastatingly efficient inside the three-point line all year and posting a 60.3/42.9/72.2 shooting split in January. Here's his shot chart for the entire season.

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Leonard was the most efficient post-up player in the league last season and has nearly doubled his output this season without lessening its effectiveness (he's now plummeted all the way down to second in post-up efficiency, according to mySynergySports).

He's also isolating more often (an area he's much improved in, turning it over just 2.6 percent of the time), and has the ball in his hands more often in the pick-and-roll, with an opportunity to make reactionary decisions instead of conclusive no-brainers.

Leonard's numbers are down, but he's gobbling up every scrap of meat Spurs head coach Gregg Popovich throws in his general direction.

Still, this was supposed to be the year Leonard's name was considered for the All-Star game. Instead he's probably still the fourth most valuable player on his own team (granted, that team is a preposterously unstoppable machine).

He's still special, and last season's Finals performance is light years away from the word "fluke." But midway through this season Leonard's numbers aren't what we expected them to be. They'll get there soon enough.

Harrison Barnes

After transforming into a 20-year-old, mismatch-creating bazooka during the 2012-13 playoffs (in particular a six-game second round battlefield against the Spurs that still causes Tony Parker to weep), it was only natural that Harrison Barnes would once again be the Warriors starting small forward on opening day this season.

Instead the team acquired peerless defensive savant Andre Iguodala, and Barnes was shoved to the bench for the first time in his brief career. The result has been great for the Warriors, but disastrous for Barnes. 

As five-time NBA champion Steve Kerr pointed out during TNT's broadcast of Monday's Warriors-Pacers game, Barnes' responsibilities have increased even as he was demoted from the starting lineup. He's 21 years old and a primary option off the bench. Being apart of the starting lineup would be better for his development, though.

For every 10 minute span Barnes is on the court, there's one where he's without any of the team's regular starters (132 total minutes). Even though the sample would be larger had Iguodala not missed extended time due to a hamstring injury, it's still pretty small. But Barnes has spent it struggling in horrific fashion.

This is what he looks like trying to carry Golden State's bench unit. Isolation heavy stuff that's not fun in the least; watching it on a full stomach is not suggested.

Barnes is averaging 8.2 points on 39.2 percent shooting in 24 games off the bench. His usage rate is the same as the 15 games where he's filled in for an injured Iguodala, and his playing time has been falling. With good reason.

Golden State's offense is a whopping 15.9 points per 100 possessions better when he's off the floor. The defense ranks second or third best when he sits then jumps to about 10th in the league when he plays, per NBA.com/Stats.

Barnes has scored at least 20 points only three times this season, a barrier he hopped over four times during last season's playoffs. His three-point shooting is up, but that's about the only good thing that can be said; almost all his per 36 minute numbers are either down from last year or the same.

The defensive end hasn't been as bad, but that's far from saying he's been good. Barnes has a rough time defending high screen-and-rolls, which is problematic considering how often he does it (opposing ball-handlers are scorching Golden State to the tune of 56.5 percent when Barnes defends them in a pick-and-roll, according to mySynergySports).

He runs directly into the pick way too often, and has a tendency to either jump above the screen defending guards who can't shoot or slink below it when facing those who can.

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Here he is guarding Dallas Mavericks point guard Jose Calderon, one of the best shooters in basketball. Instead of going above the screen, then using his length and athleticism to hound Calderon from behind and push him towards Andrew Bogut -- whose arms are less cuddly than a polar bears -- he crashes into it, then tries to slink underneath. Calderon says, "Thanks a lot, Harrison!" and pops a wide open jumper.

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The Warriors are contenders right now, with or without Barnes. That does not mean he can't someday become a very good NBA player. But before the season began it was worthwhile to ask whether the team should keep him or Klay Thompson long-term, knowing it'd be very difficult to re-sign both once their rookie scale deals expired. That question now has an answer, and any rebuilding team that's accumulated a bunch of tradable assets (the Boston Celtics, for one) should be paying attention.

Jimmy Butler

Last season, the great silver lining that emerged from the shadows of Derrick Rose's knee injury was Jimmy Butler, a herky-jerky two-way marvel who hit some threes, scored out of the pick-and-roll and flashed a rare combination of size and speed to competently defend three different positions for 74 minutes every game.

For Rose's second injury, there are no silver linings. The Chicago Bulls are overworked, exhausted and justifiably depressed. Butler's expectations were never on Leonard's level, but before the season started he was going to be a starting two-guard on a championship contender. That idea crashed and burned with Rose, but Butler hasn't exactly filled any voids. He's three years older than Harrison Barnes and two years older than Kawhi Leonard, making his stumble the most concerning of the three.

The defensive expertise hasn't gone anywhere, but Butler's somehow gotten worse with the ball in his hands. His pick-and-roll action has devolved into an array of missed jumpers, miserable rides to the rim, and turnovers. Lots and lots of turnovers (18.3 percent of the time to be exact, per mySynergySports).

His usage rate is up 3.3 percent from last year, but he still hasn't been able to create opportunities for others, which is precisely what the Bulls need from him. Instead he's averaging 2.1 assists and 1.7 turnovers per game.

Butler's shooting 37.3 percent from the floor with a PER that's dropped below league average. More than a fifth of all his field goal attempts this season (22 percent) have come from behind the three-point line on the right side of the floor (corner and above the break). That's not such a good thing for someone who should be developing as Chicago's long-term secondary ball-handler/scorer next to Rose. Shooting 27.1 percent from that area just makes it that much worse.

The good news is Chicago believes in Butler. Despite playing for a team ranked 28th in fast break points and pace, Butler is the fifth most efficient player in the entire league scoring in transition, according to mySynergySports.

He also never gets tired -- on the surface, at least -- and Chicago's support serves support serves as a partial explanation for why fan/coach/team-favorite Luol Deng was unceremoniously traded. Unless Rose retires, Butler will be a Bull for a long time.

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It isn't fair or wise to make long view critiques about any player in his early 20s, especially ones as gifted as Leonard, Barnes and Butler. Their statistical static gives no indication that they've already peaked or are headed in the opposite direction, but each was good enough to enter this season with high expectations, and none of the three has come close to meeting them.

For basketball players, the word "improve" lies next to the word "hope." But the promise of a player getting better over time because of accumulated experience, thousands of hours doing drills in a gym and individual evolution isn't a promise at all. All players develop in some way, shape or form. Some do it faster than others.

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Michael Pina is a writer from Boston who lives in Los Angeles. His work appears at ESPN, The Classical, Bleacher Report, and Boston Magazine. Follow him @MichaelVPina.