Constant incremental growth throughout a player's career is rare. Adversity often strikes and derails success. 

So, a rookie who took the league by storm won't necessarily have an easy time during his second season. Many regress. The key is getting them back on track. 

Identifying what slowed a slumping sophomore will determine whether he can break out during 2018's second half. 

Injuries often cause developmental hiccups. Something nagging tends to make individuals less explosive and reliable. These players are usually in and out of the lineup and can't build consistency or comfort level. In a league where no one's 100 percent, dings can be mere bumps in the road toward further success, or they can be debilitating.

Lineup changes also occur. Maybe a young veteran is no longer performing as well and another makes a case to play more. NFL rosters continually shift.

Coaching switches can be particularly devastating. Each staff has its own set of schemes and philosophies. Finding the right ways to use certain talents can be difficult. 

All of these can result in the same problem: an unexpected drop-off in play or production after flashes of promise. 

These seven talented sophomores were supposed to be key cogs this year, only to disappoint. But the season is far from over, and each has the ability to turn his campaign around.

Carl Lawson, Cincinnati Bengals

A slump can be somewhat subjective. Carl Lawson is a highly effective player. He continually creates pressure on opposing quarterbacks. However, his sack and usage rates aren't at expected levels. 

Lawson led all rookies last season with 8.5 sacks and 59 pressures, per Pro Football Focus. He'll have trouble eclipsing either of those numbers based on his start to the season, and a single sack as a sophomore is concerning.

Most surprisingly, the Bengals wanted to feature Lawson in the regular defensive rotation after they picked their spots with him in 2017. The coaching staff moved him from strong-side linebacker to a more traditional edge-rushing role. 

"I think in [defensive coordinator Teryl Austin's] vision, he sees the opportunity to utilize Carl more in the base defense than what we did with [former coordinator] Paul [Guenther]," head coach Marvin Lewis said during the annual league meeting, per the Cincinnati Enquirer's Paul Dehner Jr. 

Even with the shift, the Bengals still believe in the less-is-more approach. 

"The biggest thing that was true for Carl from Auburn, and that is still true after his first season, is that by limiting his exposure we are going to get more production," Lewis told reporters in August.

Well, it's not working. Jordan Willis and even veteran Michael Johnson have received more snaps at points this season. As a result, Lawson's production isn't quite to last year's level. 

The solution is simple: Play Lawson more to maximize his effectiveness. 

Corey Davis, Tennessee Titans

For one glorious afternoon, Corey Davis looked like the wide receiver the Tennessee Titans expected him to become when the organization used the fifth overall pick in the 2017 draft on him. 

Davis caught nine passes for 161 yards during a Week 4 win over the Philadelphia Eagles. 

"We all knew the athleticism and the talent that this guy has," safety Kevin Byard said after the contest, per the Tennessean's Luis Torres. "I think that game is going to be the springboard game for him in his career to understand that you can beat anybody. You're a great receiver. That's why they drafted you fifth overall, and continue to show it every day because that's what we need."

It didn't serve as a springboard, though. His receiving yardage decreased in each of the subsequent three contests. In fact, Davis managed a meager 83 yards during that stretch. 

But the talent is obvious, and quarterback Marcus Mariota wants to feed him the football. 

"I love that guy," Mariota said. "... He has to continue to have that same mindset, and if he does, he can be very successful."

Davis struggled as a rookie primarily because of a lingering hamstring injury. This year, the opposite has happened.

He's Tennessee's leading receiver with 395 yards, but the number is skewed thanks to that Week 4 performance. Defenses have held Davis under 50 yards in four of seven contests. But injuries to Mariota and the offensive line have hindered the Titans' 30th-ranked air attack. 

As the unit's health improves, so should Davis' numbers. 

David Njoku, Cleveland Browns

Cleveland Browns tight end David Njoku is easily one of the league's most infuriating players to watch. 

The 2017 first-rounder is a mismatch waiting to happen. His raw athleticism and natural ability are spectacular when he's on the field and making difficult receptions.

Yet, Njoku has consistently dropped passes throughout his first two seasons. At times, it seems like the more difficult throws make it easier for him, because he doesn't suffer from lapses in concentration. 

Even head coach Hue Jackson poked fun at Njoku after the player snagged a touchdown reception against the Los Angeles Chargers on a simple fade route. Jackson said they threw the same ball last year six times and he never made the catch, according to the Akron Beacon Journal's Nate Ulrich. 

Consistency is the biggest factor for Njoku. Some drops will happen, but he knows what to expect from the quarterback position now. 

The Browns are set with this year's first overall pick, Baker Mayfield, behind center. The reigning Heisman Trophy winner has loved to lean on his tight end, dating back to his Oklahoma days. 

As ESPN's Field Yates noted, Njoku has 22 catches for 228 yards and a pair of touchdowns in Mayfield's four games as the starter. The second-year tight end had a meager 33 yards and no scores while Tyrod Taylor was the starting signal-caller for the first two contests. 

Mayfield to Njoku should be a popular pairing this season and beyond.

DeMarcus Walker, Denver Broncos

Sometimes players get caught in numbers games. That's what's happened to Denver Broncos defensive lineman DeMarcus Walker.

"D-Walk, he's had a good camp and he's working hard every day," head coach Vance Joseph said at the beginning of the month, per CBS 4 Denver's Zack Kelberman. "It's a deep, experienced room and we only dress five guys. ... His time will come, but right now we've got five guys playing really good football. So, not his fault."

After being a healthy scratch through the first six weeks, Walker was activated for last Thursday's contest against the Arizona Cardinals. The defensive end only played a handful of snaps yet registered a tackle and recovered a fumble. 

"I got a feel for it," Walker said of his return to the lineup, per the Denver Post's Ryan O'Halloran. "I wish I can get more [playing time] to get back into the groove. I just had to make the most out of what I got."

Walker's previous absence is perplexing. 

First, the defensive front hasn't played well. In fact, Denver claims the NFL's second-worst run defense. It's understandable to play more experienced alternatives if they're performing well. But they're not. 

Second, Walker flashed during his rookie campaign despite playing out of position.

The Broncos must see how he performs in an expanded role. At worst, he's an ideal sub-package option. 

Pat Elflein, Minnesota Vikings

Minnesota Vikings center Pat Elflein is rounding into football shape. 

Elflein started 16 games last season, including the playoffs, but began this year on the physically unable to perform list after he suffered a broken ankle during the NFC Championship Game. 

The 2017 third-round pick didn't return to the starting lineup until Week 4, but he's improved in each game since. 

"We've had some tough opponents. There is always room to get better, and it just starts on the practice field and getting better," left tackle Riley Reiff said earlier this month, per the Star-Tribune's Sid Hartman. "[Elflein] brings a lot to our offensive line, and it's good to get him back in there and all of us working together."

A starting center's return can have a drastic effect on the offensive line, especially a struggling group like the Vikings featured earlier in the season. 

It's not simply about the blocks Elflein makes, even though those are important. He's also the one calling the protections and pointing out anything he sees along the defensive front. Communication is critical for any successful starting five. 

The second-year pivot showed how integral his presence is with two blocks that sprung Latavius Murray's touchdown runs Sunday against the New York Jets. 

It's not a coincidence the Vikings' two best rushing performances came in the last two weeks with Elflein up to speed. 

Leonard Fournette, Jacksonville Jaguars

Soft-tissue injuries are the worst. They take forever to heal, and the probability of reinjury is high if a player is rushed onto the field. 

The Jacksonville Jaguars took it slow after Leonard Fournette aggravated his hamstring injury in Week 4 against the New York Jets. He's not expected to return until after Jacksonville's bye in Week 9, according to ESPN.com's Adam Schefter.

But the Jaguars' actions may point toward a longer timetable. They traded for Carlos Hyde so the offense can continue to pound the football. 

Fournette's health is one of Jacksonville's top priorities. Hyde will allow last year's No. 4 pick to take the time needed to heal. 

Once healthy, Fournette can be the back the team saw last year when he rushed for 1,040 yards. 

More importantly, his physical, downhill brand of football is necessary to offset Jacksonville's shortcomings at quarterback. Blake Bortles can excel when an effective running game protects him. He can't carry the offense, though. 

Fournette must return as the team's bell cow if Jacksonville has any hopes of making the playoffs after playing in last season's AFC Championship Game. 

"It's like we're still the same team besides having D.J. [Hayden] and Leonard Fournette down," safety Tashaun Gipson said, per the Florida Times-Union's John Reid. "For the most part, we're starting to get guys back. We're still the same team. We just need to figure it out."

Solomon Thomas, San Francisco 49ers

The San Francisco 49ers are finally figuring out how to properly use 2017's third overall pick, Solomon Thomas. 

He isn't a full-time defensive end. He's an early-down edge defender best suited to the interior in sub-packages. 

Unfortunately for him, the 49ers invested a pair of first-round picks in other defensive linemen (DeForest Bucker and Arik Armstead), which is why it's taken the coaching staff so long to put him in the right position. 

"We're very fortunate," defensive coordinator Robert Saleh said in September, per The Athletic's Matt Barrows. "We've got a lot of interior guys that are pretty freaking good, and the first dibs went to, obviously, [Buckner and Armstead]. The guy that some people aren't mentioning, either, is Sheldon [Day]."

All of those players took reps from Thomas since he's athletic enough to play the edge—even though he's never shown a consistent pass-rush presence from that alignment. 

However, the 49ers have changed their approach. According to SB Nation's Oscar Aparicio, Thomas played a season-high 15 interior snaps Sunday against the Los Angeles Rams and made three defensive stops. 

A clear comfort level exists when Thomas is allowed to exploit mismatches against interior blockers instead of being overwhelmed by bigger, longer offensive tackles. Yes, the 49ers have significant investments in Armstead and Buckner, but one—Armstead, in particular—can move aside and allow a more effective option to take his place.