The second half of the 2018 NFL preseason kicks off on Thursday night, but we've already seen enough to get an initial read on most of the league's first-year players. 

Some look the part, but many others have yet to find their sea legs at the professional level. 

Without overreacting, we are able to draw some early conclusions as September looms. A lot can change, but here's what we're making of some of the NFL's most disappointing rookie preseasons to date.

Baltimore Ravens QB Lamar Jackson

How he factors in

When the Baltimore Ravens used a first-round pick on quarterback Lamar Jackson back in April, it was an indication that the ice was getting thinner underneath highly paid starter Joe Flacco. But everyone knew Jackson would probably need some time to adjust and develop at the NFL level. He's entrenched as a backup who might see some action when the offense decides to get funky, but Flacco is the guy. 

What's wrong?

Nothing, if you subscribe to the theory that he's not ready to play. The Louisville product has completed just 42 percent of his passes in three preseason outings. He's done some nice things with his legs, but he's also taken six sacks and is averaging just 4.7 yards per attempt, despite playing mainly against backup defenders.

"I don't feel like I've performed at a high level yet," Jackson said after struggling Monday night against the Indianapolis Colts, per ESPN.com's Jamison Hensley.

What it means

That, indeed, he isn't ready. Jackson made waves while putting on a show during training camp, but watching him live against hostile defenses in the preseason has confirmed Flacco doesn't have to worry about his job right now.

Tampa Bay Buccaneers RB Ronald Jones II

How he factors in

Tampa Bay Buccaneers second-round rookie running back Ronald Jones II has received plenty of praise and generated quite a lot of hype this offseason. He was never guaranteed a starting role with Peyton Barber and Jacquizz Rodgers on the roster, but there's been little doubt he'd play a major role in 2018.

What's wrong?

While Barber has averaged a strong 5.3 yards per carry, Jones has struggled. He has just 11 yards on 12 attempts, and he's yet to catch a pass. That's a concern because it might give Rodgers an edge for third-down duties. 

"In college," Bucs running backs coach Tim Spencer told ESPN.com's Jenna Laine, "there’s probably a reason they only threw to [Jones] 17 times."

What it means

Running backs can't really afford to stumble out of the gate. You expect a rookie second-rounder to make an impact immediately, especially if he's coming off three productive years as a starter in the Pac-12. The USC product is losing favor by the day, and with Barber looking superb, fantasy drafters might want to take Jones off their cheat sheets.

Cleveland Browns RB Nick Chubb

How he factors in

Like Jones, running back Nick Chubb entered his first offseason as a second-round pick looking to supplant a veteran starter. Six weeks before drafting him, the Cleveland Browns gave Carlos Hyde a three-year, $15.3 million contract, and pass-catching back Duke Johnson continues to be in line for a big role. Still, early in training camp, ESPN.com's Pat McManamon wrote that "it would not be surprising to see Chubb get the bulk of the every-down carries."

What's wrong?

The Georgia product is averaging just 2.5 yards per carry and has caught three passes for a mere 12 yards. He did break off a couple big first-down runs in Cleveland's second preseason game, but eight of his 11 carries gained two or fewer yards. That lack of consistency could be problematic. 

"Chubb played in some big-time games in college, but he's not running confident tonight in his NFL debut," tweeted NFL draft analyst Dane Brugler during that first preseason game, in which Chubb gained just 11 yards on 15 carries.

What it means

His trajectory is at least more promising considering that he's coming off a much better performance in preseason Week 2 than that effort he put together one week prior. Still, Hyde and Johnson are averaging a combined 6.2 yards per carry, and the Browns have invested much more deeply in those vets. If Chubb doesn't explode in the next couple weeks, he might be buried to start the regular season. 

Seattle Seahawks RB Rashaad Penny

How he factors in

The obvious assumption in the spring was that Rashaad Penny would wind up as the lead dog in the Seattle Seahawks' backfield. After all, the team spent a first-round pick on the enticing former San Diego State running back, and the Seattle backfield has been wide open ever since the end of the Marshawn Lynch era. 

What's wrong?

The No. 27 overall pick had just 16 rushing yards on eight carries and caught just two passes for seven yards in Seattle's preseason opener. Then he went down with a broken finger and missed the team's second exhibition affair. In the meantime, second-year seventh-round back Chris Carson has impressed and taken the reins in that backfield. 

What it means

This is probably tough luck more than anything else. Penny dominated with 2,248 rushing yards, 25 total touchdowns and 7.8 yards per carry as a senior in the Mountain West Conference. He has tremendous vision and patience, and he ran a sub-4.5 40-yard dash at 220 pounds at the combine. He's a stud, and it's only a matter of time before he makes a tremendous impact.

Carson has earned the top spot on the running back depth chart, but that isn't an indictment on Penny, because he hasn't been healthy. His weight is worth monitoring—he's now up to 236 pounds, according to ESPN.com's Brady Henderson—but as long as that doesn't become an issue, the 22-year-old should eventually excel.

Baltimore Ravens WR Jaleel Scott

How he factors in

The Baltimore Ravens receiving corps is deeper this year than in recent seasons, but you still figured Jaleel Scott would have a chance to earn a semi-significant role when the team drafted the 6'5" former New Mexico State wideout in the fourth round. 

What's wrong?

Scott has caught just one of the five passes thrown his way in three preseason games. And according to WNST's Luke Jones, he played just three snaps on offense in Monday night's exhibition matchup with the Indianapolis Colts (dropping a pass on one of them). A recent report from Jeff Zrebiec of The Athletic Baltimore (via Rotowire/CBS Sports) suggested the 23-year-old could be on the roster bubble. 

What it means

It looks like they prefer fifth-round rookie wideout Jordan Lasley, who was on the field for a team-high 34 snaps against the Colts. With veteran offseason additions Michael Crabtree, John Brown and Willie Snead pretty much guaranteed roster spots and promising third-year receiver Chris Moore also looking good, Scott might only make the roster if 2015 first-round pick Breshad Perriman does not. 

Per Rotowire, that puts him in danger of becoming the first rookie fourth-round pick in Ravens history to fail to make the team. 

Green Bay Packers WR J'Mon Moore

How he factors in

Green Bay Packers rookie wide receiver J'Mon Moore compiled 127 catches, 2,094 yards and 18 touchdowns the last two seasons in the best conference in college football, making him a prime candidate to earn a top-four receiver job now that the Jordy Nelson era has come to an end in Green Bay. 

What's wrong?

The fourth-round pick out of Missouri has caught just three of the eight passes thrown his way this preseason and has been plagued by drops. That's an issue he failed to overcome in college, so you're allowed to be concerned.

"I know I'm dropping it," he said recently, per ESPN.com's Rob Demovsky. "I know that's not what I do. So I know I have to get out there and get some catches in. Something's not right."

Less than a month ago, the Green Bay Press-Gazette's Ryan Wood reported Moore was already working with the Packers' first-team offense. But Wood suggested on Tuesday that Moore is now simply fighting for a roster spot.

What it means

In a compelling piece preaching patience with Moore, Zach Kruse of Packers Wire noted that Davante Adams, James Jones and Jordy Nelson all "fought the football at times" when they were young and new. It's probably safe to guess the 23-year-old won't play a major role in 2018, but the future could still be bright for a prospect who has the size and speed to succeed. 

Buffalo Bills LB Tremaine Edmunds

How he factors in

Unlike first-round rookie Buffalo Bills quarterback Josh Allen, fellow first-rounder Tremaine Edmunds has been penciled in as a starter since the moment the Bills drafted the linebacker 16th overall. And he impressed enough early on that he was listed by yours truly in July as one of a dozen rookies already making waves.

What's wrong?

But it's often easier for a young player to stand out in practice than in games, and that's been the case with Edmunds. The former Virginia Tech star just hasn't delivered in either of Buffalo's first two preseason outings, making just one solo tackle in each game. 

Jay Skurski of the Buffalo News reported last week that "Edmunds was largely invisible" in the team's second preseason affair with Cleveland, adding, "That's been a troubling trend this summer, as impact plays have been few and far between during training camp and the first two preseason games."

What it means

Almost nothing. Edmunds just turned 20 in May and was always going to require some time to adjust to the pro game. I know we've all run out of patience these days, but it'd be prudent to wait before judging Edmunds. 

Denver Broncos CB Isaac Yiadom

How he factors in

With veteran Aqib Talib shipped off to the Los Angeles Rams, the expectation is certainly that Denver Broncos rookie third-round pick Isaac Yiadom will be able to handle key duties immediately at cornerback. 2017 third-round pick Brendan Langley, who has struggled, and veteran Tramaine Brock, who hardly saw the field last year with the Minnesota Vikings, are the only other options beyond starters Chris Harris and Bradley Roby. 

What's wrong?

The Boston College product was picked on often in each of Denver's first two preseason games, and he took two big penalties last week against the Chicago Bears.  

What it means

That he "needs more work" in man coverage, just as NFL.com's Lance Zierlein wrote in his scouting report ahead of the draft. Yiadom has the size and physicality to become a great NFL corner, but it's clear he has a lot of developing to do. 

The Broncos gambled tremendously when they traded Talib, and now Brock is dealing with a hamstring injury, Yiadom and Langley aren't ready, and they're left extremely thin at cornerback. Oops.