The 2019 NFL free-agency market moved rapidly as soon as the legal tampering period opened. Players struck record-setting deals in quick order, and most of the top names left the market as soon as they could officially sign. 

Some teams improved more than others. But we're not focused on an organization's full list of moves. Even a notable upgrade at a single position can greatly affect an entire unit, depending on the significance of the difference between old and new.

We've identified which free-agent additions qualify as such across the NFL landscape. While some teams inked multiple players who could qualify for the list, we limited each to one appearance and looked only at signings, not trades. The combination of production, upside for transcendent performances and consistency between the prior starter and the new signee helped form the rankings.

Now, let's dive into the 10 most significant upgrades.  

10. Ja'Wuan James, RT, Denver Broncos

The 2018 Denver Broncos offensive line quickly became a shell of itself as injuries piled up. The rushing game was excellent, but the passing game finished 25th in yards per attempt as Case Keenum couldn't buy enough time to let routes develop. To fix the issue, the team upgraded from Jared Veldheer to Ja'Wuan James.

While James has similar durability concerns, he's five years younger and a much better athlete. He'll augment the Broncos' rushing attack as an outside zone blocker for Phillip Lindsay. But more importantly, he'll be counted on to keep Joe Flacco clean.

Flacco's limited mobility makes James' margin for error smaller. But the finesse-driven tackle is a talented combatant in hand battles and can mirror most rushers who use speed to win. He's not an elite blocker, but the Broncos raised both the floor and ceiling of their offensive line by landing the premier right tackle on the market.

9. Sheldon Richardson, DT, Cleveland Browns

The Cleveland Browns wisely added defensive tackle Sheldon Richardson, who was a dominant player the last two years despite putting only 5.5 total sacks on his resume. The 28-year-old will immediately play next to a tremendous set of talent in Myles Garrett, Olivier Vernon and Larry Ogunjobi. Opposing offensive lines will dread this unit all year.

The addition of Richardson is especially significant.

He'll take the place of Trevon Coley, a player better served as a depth piece rather than a starter. When offenses decide to double either Richardson or Ogunjobi, they'll be at severe risk of the other penetrating into the backfield with ease.

With 36 quarterback pressures in 2017 and 47 in 2018, Richardson was this class' only dynamic defensive tackle still in his prime. The Browns will be getting the best out of him due to his talent and their unique ability to get him into one-on-one matchups. Statistically, he could have a breakout season next to the immense talent joining him on the line.   

8. Rodger Saffold, G, Tennessee Titans

Already boasting one of the stronger run games last year, the Tennessee Titans knew they had to continue investing in their offensive line to improve. The sixth-ranked rushing line also surrendered the 10th-most sacks, which mandated some change.

The Titans splurged on the market's only top-notch guard: Rodger Saffold.

The former Los Angeles Rams left guard is a considerable upgrade in front of Marcus Mariota. He's strong enough to hold his own when on an island in pass-blocking, and his hand technique has dramatically improved from early in his career. His instant-impact ability was unrivaled in this class.

New offensive coordinator Arthur Smith was non-committal toward sticking with zone-heavy concepts in his initial press conference. That's a concern, as Saffold and the rest of the line fit that system best over more gap tendencies. But Saffold's pass blocking still makes him a massive upgrade over 2018 starter Quinton Spain.

7. Adrian Amos, S, Green Bay Packers

The Green Bay Packers aggressively addressed their most pressing defensive weaknesses, adding safety Adrian Amos and pass-rushers Preston Smith and Za'Darius Smith. Both pass-rushers have an argument they're the most significant upgrade for the Packers, but Amos' presence brings needed stability to what was a terrible unit last year.

The team managed to add some explosiveness and reliability.

Amos is a significant upgrade over the 2018 trio of Ha Ha Clinton-Dix (traded to the Washington Redskins mid-season), Kentrell Brice and Josh Jones. His coverage ability is what's most important for the Packers. Amos has ranked among the top 10 safeties in coverage grade each of the last two seasons, per Pro Football Focus.

He's not a single-high safety, and the talent around him in Chicago may have elevated his play. But the Packers will still be happy with his high floor.

His 15 combined interceptions and pass breakups over the last two years aren't impressive, but he's comfortable playing in zone and man from the safety and slot positions. Defensive coordinator Mike Pettine will rest easier knowing one safety will constantly be where he should.

6. Jordan Hicks, LB, Arizona Cardinals

For years, the Arizona Cardinals have failed to unearth a legitimate long-term middle linebacker who fits the modern landscape. Having a run-thumper who comes off the field on obvious passing downs has next to no value now, and the Cardinals finally upgraded with Jordan Hicks.

Though he's missed 21 games in his first four seasons, Hicks is one of the most dynamic interior linebackers in the NFL.

He set career highs with 91 tackles and three sacks in 2018 despite only playing in 12 games. His presence bolstered the middle of the Philadelphia Eagles defense as injuries piled up around him. Set to turn 27 this summer, Hicks' best days could be in front of him if he can just stay healthy.

He joins an athletic defensive front in Arizona and should thrive in space behind Corey Peters and Chandler Jones. The combination of Josh Bynes and Gerald Hodges was too limited, but there's a reason Hicks has Pro Football Focus' second-best coverage grade since 2015. He's, fast, rangy and instinctive, which is everything this unit has needed.

5. Bradley Roby, CB, Houston Texans

Even coming off a surprising regular season and playoff appearance, the Houston Texans entered the offseason in need of serious retooling. Their secondary had issues with age, scheme limitations and redundant skill sets. Replacing Shareece Wright and Kareem Jackson with Bradley Roby helps alleviate several of those concerns.

Roby's a dynamic man-coverage corner who allows the Texans to lessen the predictability of 2018's zone-based scheme. Neither Wright nor Jackson had the fluidity or speed to stick with receivers on sharp cuts or downfield routes, which forced defensive coordinator Romeo Crennel's play-calling.

That shouldn't be as much of an issue with Roby on the roster.

The position makes more sense now that he and Tashaun Gipson have traded places with the aforementioned corners and Tyrann Mathieu. Slot corner Aaron Colvin will return to his natural position and compete with Briean Boddy-Calhoun. Landing their No. 1 corner in Roby makes everything easier throughout the rest of the secondary.

4. John Brown, WR, Buffalo Bills

It was no secret the 2018 Buffalo Bills had one of the least desirable sets of playmakers in the league around rookie quarterback Josh Allen. The breakouts of Zay Jones and Robert Foster into worthwhile rotational players were at least encouraging, but they needed more for the offense to continue growing.

They signed veteran receivers John Brown and Cole Beasley in free agency, and that accomplished their mission.

The acquisition of Brown is especially notable as a significant upgrade for this offense. Foster emerged as a downfield threat, but Brown's much more reliable and dynamic adjusting to the ball in the air. That's a must with Allen at quarterback.

His blend of downfield speed, sharp cuts and play strength re-established Brown as a legitimate starter after he struggled with consistency and injuries in Arizona. The change to Lamar Jackson at quarterback limited his production down the stretch, but Bills offensive coordinator Brian Daboll should treat him as the primary receiver for Allen's progressions.

If given the opportunity in 2019, he could set career highs in receptions and yards.

3. Trent Brown, LT, Oakland Raiders

The Jon Gruden era has certainly led to some interesting results thus far.

After moving a solid left tackle in Donald Penn across the line to open a spot for first-round reach Kolton Miller, he quickly abandoned the idea of Miller playing on the left when he signed Trent Brown to the richest offensive lineman deal in NFL history. The signing means Brandon Parker—a third-round pick in 2018—will become a backup after starting 12 games during his rookie season.

Brown benefitted from playing with Tom Brady and working with an elite offensive line coach in Dante Scarnecchia, but he's an upgrade for the Raiders.

The massive tackle was ranked 44th overall by Pro Football Focus on throws over 2.6 seconds. Parker and Miller were ranked 72nd and 74th, respectively, among the 74 qualified players. While that doesn't seem to justify the price tag, Oakland needed help at the position, and Brown was the best available.

The painstaking process of developing young blockers clearly impeded Gruden's ability to build a quality offense last year. He deserves credit for identifying his error and fixing it, and coming away with Brown will help the Raiders' short-term outlook.

They shouldn't expect Brown to be a Pro Bowler, though.

2. Le'Veon Bell, RB, New York Jets

Choosing the most significant upgrade for the New York Jets wasn't easy. C.J. Mosley is a significantly better run defender and more consistent presence than Darron Lee. Kelechi Osemele, in a gap scheme, puts Jonotthan Harrison back at center.

Both are tremendous pickups for the Jets, but they don't quite make the leap Le'Veon Bell does.

The transcendent back replaces Isaiah Crowell, who is serviceable but has mediocre upside on any given week. A defense that keyed in on Crowell could slow his effectiveness and bog down the Jets offense.

Bell's 2017 season brought reduced explosion, but he was still elite on a per-touch basis. While rushing for 1,291 yards, he averaged 7.7 yards per catch and accumulated 85 receptions. He's the perfect weapon for second-year quarterback Sam Darnold.

His patience and ability to avoid direct contact will serve him well as he ages within Adam Gase's offense. Gase runs a mixed run scheme with a healthy dose of inside zone, which fits the blocking personnel well. Bell's used to that, and he never leaves meat on the bone.

1. Trey Flowers, DL, Detroit Lions

The only premier pass-rusher in his prime to hit the market this year was former New England Patriot Trey Flowers. The versatile defender landed with the Detroit Lions, who received only 21 sacks from their defensive linemen in 2018.

Flowers, capable of playing at end and tackle, is just 25 years old.

He's replacing the old and broken-down Ezekiel Ansah, who had just four sacks in limited action last year. Flowers has produced 21 over the last three seasons, but he's constantly been in the backfield as a sack-opportunity creator for his teammates. He was responsible for 78 total pressures on 581 pass-rushing snaps last year, per Pro Football Focus.

His run defense is also a massive boost to a unit that ranked 16th in yards allowed per carry. Flowers will affect Detroit's entire front seven even if his sack production isn't significant. Fellow pass-rushers Kerry Hyder and Romeo Okwara will benefit from his presence.