For the most part, NFL fans can recognize who the established stars are on each team. Everyone knows that  quarterback Aaron Rodgers makes the Green Bay Packers offense hum. It's not difficult to see that the Los Angeles Chargers defense is based around pass-rushers Joey Bosa and Melvin Ingram.

What isn't as obvious is which non-established players have the potential to change a team's course. New additions, breakout players, guys returning from injury—they can all make a squad significantly better than it was a year ago.

Just look at the way rookie quarterback Baker Mayfield changed the complexion of the Cleveland Browns in 2018 once he got on the field and in an offense he was comfortable running. Or how tight end George Kittle exploded onto the scene to give the San Francisco 49ers a surprisingly elite receiving talent. Or how cornerback Jason McCourty emerged in the New England Patriots secondary to help spark another Super Bowl run.

None of these players were stars prior to the 2018 season, but each managed to provide a positive impact in a relatively unexpected way. They were the X-factors for their respective teams, and each franchise has its own such guy heading into 2019.

These are the players we'll be examining here.

Arizona Cardinals: QB Kyler Murray

Quarterback Kyler Murray is unproven as an NFL player. However, the Arizona Cardinals are confident the 2019 No. 1 overall pick can have the kind impact that Mayfield had for the Browns as a rookie last season. There's plenty of reason for them to believe this. The Oklahoma Sooners product is one of the most dynamic signal-callers we've seen coming out of college in recent years.

In his lone season as a starter, Murray racked up 4,361 passing yards, 1,001 rushing yards and 54 total touchdowns.

With new head coach Kliff Kingsbury looking to bring his uptempo offense to the Cardinals, Murray becomes the biggest X-factor. The season is going to go as Murray goes, for better or worse.

Atlanta Falcons: RB Ito Smith

There are two reasons why running back Ito Smith will be an X-factor for the Atlanta Falcons in 2019. The first is that Tevin Coleman left in free agency. The second is that starting back Devonta Freeman is coming off an injury-shortened campaign.

The Falcons need to have a strong rushing attack to take some pressure off the shoulders of quarterback Matt Ryan and to balance out the offense. Smith can help, both by replacing Coleman and complementing Freeman in the backfield.

While Smith only averaged 3.5 yards per carry as a rookie in 2018, he did catch 27 passes and found the end zone four times. He is the next man up in the running game, and a strong season from Smith should help the Falcons put their disappointing 2018 campaign behind them.

Baltimore Ravens: WR Marquise Brown

Oklahoma's Marquise Brown was the first receiver taken in the 2019 draft. The No. 25 overall selection has true game-breaking speed and should emerge as the Baltimore Ravens' No. 1 wideout sooner rather than later.

However, there are some concerns. Brown is an undersized receiver at just 5'9", 166 pounds, and he's coming off a Lisfranc surgery. However, the Ravens expect him to be ready by the start of the regular season.

"My expectation is that he'll open training camp," head coach John Harbaugh said, per the team's official website.

If Brown is back to 100 percent, he'll potentially change the way the Ravens are able to attack opposing defenses. They will have to respect his elite speed, and that will open things up for second-year quarterback Lamar Jackson as well as Mark Ingram II and the rest of Baltimore's rushing attack.

Buffalo Bills: TE Tyler Kroft

Last year, the Buffalo Bills did not have a security blanket at tight end to aid in quarterback Josh Allen's development. They signed Tyler Kroft—who had 404 receiving yards and seven touchdowns two seasons ago—to help remedy this.

However, Kroft is coming off a season that ended with him on injured reserve, and he suffered a broken foot during OTAs.

This makes Kroft a wild card. If he's able to get back to his 2017 form by the start of the season, he'll give Allen that much-needed safety valve in the passing game. If not, Buffalo will have to consider other options, such as rookie tight end Dawson Knox.

Carolina Panthers: DE Brian Burns

The biggest question for the Carolina Panthers this season is whether quarterback Cam Newton will be healthy. Aside from that, though, it's whether the Panthers can field a quality pass rush.

In 2018, the team only produced 35 sacks (sixth-fewest in the league). Five of them came from recently retired edge-rusher Julius Peppers.

This is why the Panthers used the 16th overall pick on Florida State pass-rusher Brian Burns. This is also why Burns is the biggest defensive X-factor on the roster. If he's capable of having a big impact off the edge, Carolina will have a far easier time pressuring the likes of Drew Brees and Matt Ryan in the NFC South.

Chicago Bears: WR Allen Robinson

Last offseason, the Chicago Bears signed Allen Robinson to be their No. 1 receiver. However, injuries limited him to 12 games and just 754 receiving yards.

This leaves Robinson as the biggest offensive X-factor heading into 2019. Can he stay healthy? Can he perform like he did in 2015, when he had 1,400 yards and a league-leading 14 receiving touchdowns? These are questions that only Robinson can answer.

Having a true No. 1 receiver does a lot for an offense. It dictates defensive attention and gives the quarterback a go-to target in clutch situations. If Robinson can again emerge as that type of talent, he will provide a huge boost to quarterback Mitchell Trubisky and the Bears' passing attack, which ranked just 21st in the league last season.

Cincinnati Bengals: WR John Ross

Will new head coach Zac Taylor figure out how to unlock John Ross in the Cincinnati Bengals offense? This is a huge question heading into 2019.

Ross blew away the field at the 2017 NFL Scouting Combine, producing a record 4.22-second 40-yard dash. That impressed the Bengals enough to use the ninth overall pick on him. Since he's entered the league, though, Ross has all of 21 receptions for 210 yards and seven touchdowns.

If Taylor can get some consistency out of Ross, the third-year wideout will be a major X-factor. He has the speed to stretch the field and open things up for fellow receivers A.J. Green and Tyler Boyd.

Ross also has the potential to spark the offense with gadget plays. His speed can be lethal on receiver sweeps and bubble screens, and Taylor should put plenty of focus on getting the football into his hands.

Cleveland Browns: LB Genard Avery

Plenty has been written about the Cleveland Browns' additions along the defensive line (Olivier Vernon, Sheldon Richardson) and in the secondary (Greedy Williams, Morgan Burnett) this offseason.

However, the Browns still have a hole to fill at the linebacker position. They needed depth there even before parting ways with Jamie Collins after the 2018 season.

This is where Genard Avery comes into play. He showed a lot of potential as a rookie, producing 40 tackles and 4.5 sacks in limited action. The 24-year-old linebacker has the potential to improve Cleveland's run defense and its pass defense at the second level if he's able to make a second-year jump.

Dallas Cowboys: WR Randall Cobb

The Dallas Cowboys are in a good place offensively. They have an established quarterback in Dak Prescott, a workhorse running back in Ezekiel Elliott and a legitimate No. 1 receiver in Amari Cooper. What the team lacked in 2018 was a second receiver it could rely upon when defenses were able to take Cooper out of the game.

This is why the Cowboys added Randall Cobb in the offseason.

The big question is this: Which version of Cobb are they getting? In 2018, Cobb played in just nine games and had just 38 receptions for 383 yards and two touchdowns. The last time he played a full 16-game season, though—in 2015—he racked up 829 yards and six scores.

Cobb is still just 28 years old, and if he's able to be close to his 2015 version, he could be the missing piece of the offense that Dallas needs to be a title contender.

Denver Broncos: TE Noah Fant

The Denver Broncos are banking on veteran Joe Flacco to lead them to the postseason in 2019. While Flacco has floundered a bit as of late, he is still an experienced quarterback capable of playing at a high level with the right pieces around him.

One of those right pieces is a reliable pass-catching tight end. This is why rookie Noah Fant is the X-factor of the Broncos offense.

Fant was a tremendous receiving weapon at Iowa. He amassed 519 yards and seven touchdowns on just 39 receptions in 2018. If he's able to have a similar impact for the passing attack, Flacco will benefit greatly—and yes, the Broncos could be a factor in the AFC West.

Detroit Lions: DE Trey Flowers

There are two reasons why new Detroit Lions defensive end Trey Flowers will be an X-factor in 2019. The first is that he's a versatile defender capable of chasing down ball-carriers, pressuring quarterbacks and setting the edge.

Last season, Flowers produced 57 tackles, 7.5 sacks and three forced fumbles for the New England Patriots.

The second reason is that Flowers is the kind of defender head coach Matt Patricia needs to make his multiple-scheme defense work. Patricia's defense showed glimpses of promise last season but left a lot to be desired over the course of the year.

The addition of Flowers—who has some familiarity with the defense—should allow the former Patriots coordinator's unit to look a little more like the championship-caliber defenses he coached with New England.

Green Bay Packers: S Darnell Savage

The Packers made several defensive additions this offseason, including Za'Darius Smith, Preston Smith, Adrian Amos, rookie defensive end Rashan Gary and rookie safety Darnell Savage. Of the bunch, Savage is the biggest X-factor because of the versatility he brings to the Packers secondary.

He is both a quality tackler—he had 52 total tackles for Maryland in 2018—and a quality pass defender.

"His sticky cover skills and ability to close on throws from all areas of the field are valuable commodities that should not be undervalued," NFL Media's Lance Zierlein wrote prior to the draft.

Green Bay will be able to put Savage on the field in a variety of defensive situations and can expect him to make big plays in any of them. He should have an impact similar to the one Derwin James made for the Chargers a year ago—albeit with more focus on defending the pass.

Houston Texans: OT Tytus Howard

The Houston Texans offensive line was a disaster in 2018. It allowed quarterback Deshaun Watson to be sacked a league-high 62 times and exposed him to several unnecessary hits that would be alarming for a quarterback not coming off a torn ACL.

This is why rookie first-round pick Tytus Howard is an X-factor heading into the regular season. Though the Alabama State product isn't a refined prospect, his physical potential and upside are tremendous. He's quick and nimble for a 322-pound lineman and could develop into one of the league's better young tackles early in his career.

The question is whether Howard can earn a starting spot as a rookie. If he can, he should immediately improve the line in front of Watson—which will be great both for the quarterback's health and for the offense's consistency.

Indianapolis Colts: LB Justin Houston

The Indianapolis Colts defense was good enough to help spark a playoff run in 2018. However, the pass rush left plenty to be desired. The team produced a middling 38 sacks.

One of Indianapolis' biggest issues was it lacked a premier pass-rusher off the edge. That could change in 2019, though, thanks to free-agent acquisition Justin Houston.

Houston, who had 18.5 sacks over the past two years, can be the elite edge-rusher the Colts have been missing. The question, of course, is whether he'll be the same player in coordinator Matt Eberflus' defense. If he is, he could take the unit from good to great.

Jacksonville Jaguars: QB Nick Foles

Can the Jacksonville Jaguars get back to being title contenders in 2019? That will depend on new quarterback Nick Foles.

The team brought in the 30-year-old veteran to replace 2014 first-round pick Blake Bortles. Foles took the Philadelphia Eagles to the playoffs in each of the past two seasons and even helped them win their first Super Bowl, earning MVP honors for the championship game against Tom Brady and the Patriots.

Of course, Foles' track record away from Philadelphia isn't as impressive. He started 11 games for the then-St. Louis Rams in 2015 and produced a lowly passer rating of just 69. He threw just seven touchdown passes with 10 interceptions that year and was off the team after just one season.

This makes Foles an X-factor in the truest sense. He's both been a goat and beaten the G.O.A.T. prior to joining the Jaguars. The version of Foles that Jacksonville gets will go a long way toward determining the team's playoff chances.

Los Angeles Chargers: TE Hunter Henry

The Los Angeles Chargers managed to have a dynamic passing attack in 2018 even without emerging tight end Hunter Henry, who suffered a torn ACL in the offseason. However, Henry is a dangerous player whose presence would have made L.A. even more dangerous offensively.

In 2017, Henry produced 579 yards and four touchdowns while splitting time with Antonio Gates.

The good news is that Henry appears to be back to—or at least close to—100 percent this offseason.

"I'm pretty much full-go," he said in April, per Ricky Henne of the team's official website.

If Henry is indeed healthy this season, he'll be the offensive X-factor the Chargers missed in 2018.

Los Angeles Rams: RB Darrell Henderson

Given the uncertainty surrounding running back Todd Gurley II and his knee, the Los Angeles Rams may have to rely on other backs frequently in 2019.

This is where rookie third-round pick Darrell Henderson enters the equation. The Rams did retain backup Malcolm Brown in free agency, but Henderson has the potential to be the kind of dynamic running back that Brown is not.

Last season alone, Henderson racked up 1,909 rushing yards, 295 receiving yards and 25 total touchdowns for the Memphis Tigers.

On just about any other team, Henderson would be viewed as a potential rookie starter. While the Rams still have Gurley penciled in for that role, Henderson is an X-factor who could be an important part of another deep playoff run.

Kansas City Chiefs: RB Damien Williams

One of the biggest questions facing the Kansas City Chiefs heading into the offseason was who would replace Kareem Hunt at running back. The Chiefs have given us their answer.

"Damien Williams is our starter," offensive coordinator Eric Bieniemy said, per Matt Derrick of Chiefs Digest. "We expect him to excel in that role."

This makes Williams the biggest X-factor. He showed promise in limited action last season, averaging 5.1 yards per carry and catching 23 passes, and he could be a legitimate full-time starter. Should he struggle in that role, however, Kansas City will be forced to weigh other options—like Darrel Williams and offseason acquisition Carlos Hyde.

Miami Dolphins: QB Josh Rosen

Quarterback Josh Rosen is going to be an X-factor for the Miami Dolphins for a couple of reasons. For one, he's competing with journeyman Ryan Fitzpatrick to be the 2019 starter. If he wins the job and plays well, the Dolphins could surprise some folks this season.

The other piece of the equation is that Rosen could be Miami's quarterback of the future. This is why the Dolphins were willing to deal a second-round pick and a 2020 fifth-rounder to acquire him during the draft.

However, if Rosen doesn't establish himself as a starter—or if he doesn't perform at a high level in his second pro season—the Dolphins could be headed back to their draft board to fix the position next April.

Minnesota Vikings: WR Jordan Taylor

In Stefon Diggs and Adam Thielen, the Minnesota Vikings have one of the best receiver tandems in the NFL. What the team lacked in 2018 was a reliable third receiver who could exploit the defensive attention those two commanded.

This could change in 2019, thanks to the addition of Jordan Taylor.

Taylor last played for the Broncos in 2017—he spent last year recovering from hip surgery—and caught 13 passes for 142 yards. However, the Vikings like what they've seen from the Rice product so far.

"He's got some stuff to him," quarterback Kirk Cousins said, per Eric Smith of the team's official website. "Not only does he have some juice, but he’s been on the details."

If Taylor can emerge as that reliable No. 3, the Vikings' passing attack will be difficult to stop this season.

New England Patriots: DE Michael Bennett

The New England Patriots parted with defensive end Trey Flowers this offseason. Though he wasn't a traditional edge-rusher, Flowers was a versatile piece of the line who was capable of generating pressure.

To replace him, the Patriots brought in Michael Bennett, who is a bit more of a traditional edge-rushing defensive end.

This makes Bennett the Patriots' biggest defensive X-factor. Not only will he have to replace Flowers' role in the defensive front, but he'll also be asked to provide a spark to the pass rush.

Bennett had nine sacks for the Eagles last season, and if he can have a similar year for the Patriots, the defense as a whole will benefit.

New Orleans Saints: TE Jared Cook

Jimmy Graham last played for the New Orleans Saints in 2014. With all due respect to decorated veteran Ben Watson, 2014 was the last year in which the team had a dangerous receiving threat at the tight end position. Watson had just 400 yards and two scores in 2018.

The offseason addition of Pro Bowler Jared Cook, however, could change this.

Cook racked up 896 yards and six touchdowns with the Oakland Raiders last season, despite being the only pass-catcher opposing defenses had to focus on. With the Saints, he'll be the No. 2 target behind Michael Thomas, and he'll have the potential to change the way the passing attack operates.

New York Giants: S Jabrill Peppers

For a lot of New York Giants fans, safety Jabrill Peppers is probably viewed as the guy the team got in exchange for Odell Beckham Jr. However, Peppers can fill a variety of roles and will be an X-factor in 2019.

As a defender, Peppers is best utilized against the run. This means he should at least help replace departed strong safety Landon Collins in that run-support role. He is capable of making plays against the pass, though, and has snagged an interception in each of his two pro seasons.

Peppers can also provide a boost on special teams. He has experience returning both punts and kicks, and his contributions to the Giants shouldn't be limited to just defense. If the 2017 first-round pick is able to realize his full potential, New York could have a new rising star on its hands.

New York Jets: TE Chris Herndon

A great receiving tight end can help a young quarterback grow, learn and perform at a high level. This is why Chris Herndon can be an X-factor for the New York Jets in 2019.

Herndon flashed plenty as a rookie last season, catching 39 passes for 502 yards and four touchdowns. He's hungry to be even better in his second season.

"I want to improve from last year. I want to continue to do what they [the coaches] ask of me and even more," Herndon said, per Olivia Landis of the team's official website.

The 23-year-old has an important role to play as the safety valve for second-year quarterback Sam Darnold. If Herndon is able to become a top-tier tight end, Darnold's growth as a passer will get a tremendous boost.

Oakland Raiders: RB Josh Jacobs

The Oakland Raiders strengthened their receiving corps during free agency, signing Tyrell Williams and trading for Antonio Brown. In the draft, they addressed their backfield by using a first-round pick on Alabama's Josh Jacobs.

While Williams and Brown will almost certainly boost Oakland's 18th-ranked passing attack, Jacobs is the real offensive X-factor. He's a versatile back who can run hard between the tackles, create in space and catch balls out of the backfield.

If Jacobs can make the kind of rookie impact backs like Alvin Kamara, Kareem Hunt and Ezekiel Elliott have had in recent years, the Raiders offense should be a formidable and fun-to-watch unit in 2019.

Philadelphia Eagles: WR DeSean Jackson

Wide receiver DeSean Jackson may not have quite the same game-breaking speed that he possessed early in his career. However, he is still capable of stretching the field and averaged an impressive league-leading 18.9 yards per reception in 2018.

This makes Jackson's return to the Eagles a noteworthy development. He can fundamentally change the way the team is able to attack opposing defenses.

Philadelphia has big-bodied targets like Zach Ertz (6'5", 250 lbs) and Alshon Jeffery (6'3", 218 lbs). It has a quick and shifty receiver in Nelson Agholor. Adding Jackson gives the Eagles the kind of burner who can make guys like Ertz, Jeffery and Agholor even more impactful by forcing opposing defenses to play more deep coverage.

While the trade for Jackson didn't generate as many headlines as the Antonio Brown and Odell Beckham deals did, it could prove to be equally impactful.

Pittsburgh Steelers: WR James Washington

The trade of Brown means that JuJu Smith-Schuster becomes the new No. 1 receiver for the Pittsburgh Steelers. While Smith-Schuster appears to be perfectly capable of filling this role, the Steelers need someone to take over his vacated No. 2 spot.

This is where second-year wideout James Washington comes into play. He isn't the only receiver with the potential to grab the job—the Steelers drafted Diontae Johnson in the third round this year—but he flashed some promise as a rookie and could be poised for a second-year jump.

The former second-round pick averaged a strong 13.6 yards per reception in 2018, higher than both Brown and Smith-Schuster. If his Year 2 jump is even close to Smith-Schuster's last season, the Steelers should have little trouble moving on from Brown.

San Francisco 49ers: DE Nick Bosa

The San Francisco 49ers could have one of the best defensive fronts in 2019. They have former first-rounders Arik Armstead (2015), DeForest Buckner (2016) and Solomon Thomas (2017). They also traded for pass-rusher Dee Ford this offseason.

But the X-factor in the defense is 2019 second overall pick Nick Bosa.

Bosa has the potential to be the elite edge-rusher the 49ers have been missing. If he can make a quick transition to the pro game, he and Ford could forge a pass-rushing duo similar to the one Joey Bosa and Melvin Ingram have in L.A. With guys like Buckner and Armstead manning the middle, San Francisco's defensive front would then become a veritable nightmare for opposing offensive coordinators.

Seattle Seahawks: WR DK Metcalf

The Seattle Seahawks find themselves having to replace former No. 1 receiver Doug Baldwin, who retired this offseason. Tyler Lockett, who had 965 yards receiving and 10 touchdowns last season, will likely slide into the role.

This still leaves Seattle in need of complementary receivers, and rookie second-round pick DK Metcalf is an X-factor in that search. He's a bit on the raw side, but he has tremendous physical potential and is already raising some eyebrows in the offseason.

"He can do anything and everything, and he's tremendous," quarterback Russell Wilson said, per John Boyle of the team's official website.

Metcalf averaged a whopping 21.8 yards per reception in 2018. If he is able to be a similar downfield threat as a rookie, opposing pass defenses are going to be in trouble.

Tampa Bay Buccaneers: LB Devin White

There's a big reason why the Tampa Bay Buccaneers used the fifth overall pick on LSU linebacker Devin White in April. Tampa's defense was inconsistent against both the run and the pass in 2018—it ranked 24th and 26th, respectively—and White has the ability to impact both areas.

The 21-year-old has the potential to give the Buccaneers a true sideline-to-sideline playmaker at the second level. Last season alone, he produced 123 tackles, made three sacks and had six passes defended.

White can be Tampa's version of Darius Leonard or Leighton Vander Esch, guys who boosted their own defenses in big ways as rookies. He should be a Defensive Rookie of the Year candidate, and he'll give new defensive coordinator Todd Bowles a chesspiece to play with in a variety of ways.

Tennessee Titans: WR Adam Humphries

The Tennessee Titans have a strong running attack that features both Derrick Henry and Dion Lewis. They have an emerging No. 1 receiver in Corey Davis. What could potentially push the offense over the top—and perhaps finally unlock Marcus Mariota's potential as a passer—is the addition of slot receiver Adam Humphries.

Humphries had a breakout season for the Buccaneers in 2018, amassing 816 yards and five touchdowns. If he can have a similar year for the Titans, he'll give them a quality second option alongside Davis and allow Tennessee to run a more complete offense.

The Titans fell just sort of the postseason in 2018, and a more balanced offense could be just the thing needed to get them there this season.

Washington Redskins: RB Derrius Guice

While the quarterback competition between Dwayne Haskins and Case Keenum is the biggest offseason story for the Washington Redskins, running back Derrius Guice is the team's biggest X-factor heading into the regular season.

Guice was a special talent at LSU and could give the Redskins the kind of back who can carry the team week in and week out. However, Washington didn't get a good gauge of his ability as a rookie because of a torn ACL suffered in the preseason.

If Guice is back to 100 percent, Washington can employ a dynamic running attack featuring both him and Adrian Peterson.

"They are both different, but they are both explosive," running backs coach Randy Jordan explained, per Julie Donaldson of NBC Sports Washington.

With both Peterson and Guice pounding the ball, the Redskins could have a dangerous offense regardless of who is under center.