By Ryan Dunleavy | NJ Advance Media for NJ.com

Red flags come in all different shapes and sizes.

They can be physical skills. They can be on-field qualities. They can be off-field issues.

There are five quarterbacks — Josh Rosen, Sam Darnold, Josh Allen, Baker Mayfield and Lamar Jackson — commonly projected as first-round picks in the NFL Draft, and all will be on hand this week at the NFL Combine in Indianapolis.

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Chuck Cook | USA TODAY Sports

All 336 prospects at the NFL Combine will be poked and prodded ... literally and figuratively. Perhaps none more so than the top five quarterbacks.

There are drills to run, routes to throw, measurements to be taken and private interviews to be conducted.

The Giants and Jets hold the No. 2 and No. 6 picks, respectively, and both could be in the market for a quarterback if all checks out right.

Here are the red flags that each quarterback faces heading into the Combine, and NJ Advance Media's pre-Combine analysis of each.

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Kelvin Kuo | USA TODAY Sports

Josh Rosen, UCLA

Red flag 1: Durability

Red flag 2: Likeability

Must ace: Medical exams/Interviews

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Rosen has a swagger to him that will be celebrated if he becomes the next Aaron Rodgers. Before he has thrown his first NFL pass, however, his personality comes off as a lack of humility.

Rosen might be the best pure passer in the group — scouts like his footwork, accuracy and pocket presence — but he also suffered two concussions in 2017, one of which forced him out of his bowl game after he said he planned to play. He missed six games in 2016 due to a shoulder injury.

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Speculation has surfaced that teammates don't like Rosen because he is selfish — sounds a little like that Bo Callahan birthday party storyline from the movie 'Draft Day' — ... and doesn't love football ... and is hard to coach.

Rosen put a hot tub in his dorm as a freshman, gave a candidate interview about being the challenges of a NCAA student-athlete and posted a viral photo of himself wearing a 'F--- Trump' hat. Is he distracted or just outspoken?

ESPN's Mel Kiper dropped Rosen from No. 2 to No. 11 in his mock draft and said that the team interviews are going to important for Rosen to change the narratives about him.

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Kirby Lee | USA TODAY Sports

Sam Darnold, USC

Red flag 1: Turnover-prone

Red flag 2: Regression

Must ace: On-field tests/measurements

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Darnold likely would have been the No. 1 pick in the 2017 NFL Draft had he been eligible to enter — and that's despite not opening 2016 as USC's starter. Shows you how good he was during a nine-game tear, capped with a Rose Bowl win against Penn State.

Darnold was supposed to develop into an Andrew Luck-level sure thing in 2017, but he took a step backwards and stumbled in showcases against Notre Dame, UCLA and Ohio State.

He threw 13 interceptions (20 in his last 20 games) and lost nine fumbles, which has people questioning his hand size. They actually measure that sort of thing at the Combine and nine-inch hands are considered the minimum standard.

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Darnold also has an elongated delivery, which gives defenders an extra split-second to read and react to a pass. A case of "happy feet" — doesn't stay firm in the pocket under pressure — also is assigned to him.

Has Darnold made any tweaks to his mechanics since the season ended? He said during Super Bowl week he plans to throw at the Combine, but hasn't followed up with any declarations.

Darnold still is four months shy of his 21st birthday, but he mature beyond on his years and maybe a little vanilla in that Eli Manning "cool guy" way.

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Brian Losness | USA TODAY Sports

Josh Allen, Wyoming

Red flag 1: Inaccuracy

Red flag 2: Competition level

Must ace: On-field drills

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Because he has physical gifts and played against inferior competition at Wyoming, people expect Allen to have completed 80 percent of his passes. That's unrealistic, but it isn't unfair to expect a 60 percent completion rate — and he didn't reach it. Not even close (56.2 percent for his career).

Can he make up what he lacks in accuracy with uncanny arm strength? Or does confidence in his own arm lead him to make risky throws?

Allen struggled against Iowa and Oregon in 2017, when he combined to go 32-of-64 for 234 yards with no touchdowns and three interceptions. He won over some critics by finishing strong in Wyoming's bowl win and looking/sounding more polished at Senior Bowl week, outside of the shadow cast by Darnold and Rosen.

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Allen says all the right things — he is willing to sit and soak up knowledge behind Manning — but, unlike the other quarterbacks on this list, the tri-state area spotlight and pressure-cooker would be a new experience for the central California native.

Allen also an ability to scramble, either running for yards or to keep plays alive. That's made a huge difference in Rodgers' career.

He could be the biggest boom-or-bust pick in the entire first round, so he deserves extra attention.

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Sean M. Haffey | Getty Images

Baker Mayfield, Oklahoma

Red flag 1: Maturity

Red flag 2: Size

Must ace: Interviews/measurements

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It angered some when Mayfield won the Heisman Trophy in the fall despite a one-time crotch grab aimed at opposing fans and an arrest before the season for public intoxication, disorderly conduct and fleeing the scene.

Those incidents are separate from the the decision to plant the Oklahoma University flag at midfield of Ohio Stadium after beating Ohio State. Some interpret the flag-plant as another sign of immaturity detrimental to the team, while others say it's a sign of fiery winner whose teammates are drawn to his passion.

It's similar to the lens with which all of Odell Beckham Jr.'s actions are viewed, but he isn't a quarterback.

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Like Rosen, Mayfield will speak his mind. He also has a huge chip on his shoulder, after beginning his college career as a walk-on at Texas Tech.

You want accuracy? Mayfield is your man after back-to-back seasons completing more than 70 percent of his passes. He looked totally in command of his offense.

Mayfield measured just over 6-foot tall at the Senior Bowl, which makes him shorter than the others in this quintet. Drew Brees and Russell Wilson have become height concerns to become huge stars, but neither was a first-round pick. Teams need to make sure they don't wind up with the reincarnation of another Heisman winner (Doug Flutie).

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Melina Vastola | USA TODAY Sports

Lamar Jackson, Louisville

Red flag 1: Durability

Red flag 2: Size

Must ace: On-field drills

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Whereas the focus with Mayfield is on his height, it will be on Jackson's weight (200 pounds). Or, rather, his overall frame and whether it will hold up under his run-first instincts.

He already has been called a right-handed Michael Vick. The comparison is obvious because Jackson is an explosive play waiting to happen, with 10 rushing touchdowns of 40 yards or more during three seasons.

But Vick was injury-prone throughout his career. So was another recent run-first quarterback who made an immediate splash but quickly flamed out: Robert Griffin III.

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Jackson's rocket-launcher arm make the throws seem effortless — like a flick of the wrist — but he also misses targets too much, which makes it seem like maybe a little more effort would be a good thing.

The question is: Will Jackson show the patience to let plays develop? Or will he take off if his first and second reads are covered, not realizing the speed of the defense in the NFL is that much faster than in college? If he doesn't learn to slide more, owners, general managers and coaches will be holding their breath much too often.

The 2016 Heisman Trophy couldn't elevate Louisville to the top of the ACC, which might be a concern, too. He might be the most raw quarterback of the bunch, but Louisville's Bobby Petrino is a quarterback guru. So maybe Jackson is who he is, rather than a high-ceiling option.

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Ryan Dunleavy can be reached at rdunleavy@njadvancemedia.com. Follow him on Twitter @rydunleavy.com.