Over the past year, Buffalo Bills signal-caller Josh Allen made a remarkable leap from a quarterback with a lot to prove to a franchise player who could sign a lucrative extension in the near future.

Going into the 2021 campaign, Pro Football Focus lists Allen as a Tier 1 quarterback. For DraftKings' futures bets, he's tied with Aaron Rodgers for the second-best odds (+1000) to win the 2021 MVP award.

During his rise to prominence, Allen built a strong rapport with star wideout Stefon Diggs, exhibited a strong command of offensive coordinator Brian Daboll's system and had solid pass protection. He faced pressure on 21.9 percent of his dropbacks, which ranked in the middle of the pack among primary starting quarterbacks. 

Based on the aspects that propelled Allen into the spotlight, we're going to rank five potential breakout candidates (26 years old or younger) who could make the biggest strides between the 2020 and 2021 campaigns. We've excluded rookies, quarterbacks with Pro Bowl and All-Pro seasons and 2020 Offensive Rookie of the Year Justin Herbert to illustrate players who could show the most improvement.

5. Tua Tagovailoa, Miami Dolphins

Tua Tagovailoa went through his fair share of ups and downs through his rookie campaign.

In 2020, Tagovailoa helped lead the Dolphins to six wins in his nine games as a starter, completed 64.1 percent of his passes and engineered two fourth-quarter comebacks.

On the other hand, the Dolphins benched Tagovailoa multiple times. Despite his decent completion rate, he didn't stretch the field, gaining just 6.3 yards per pass attempt.

Tagovailoa admitted that he didn't have a firm grasp of the playbook. He's also said his surgically repaired hip feels "10 times" better than it did last year.

The Dolphins added big-play wide receivers this offseason, signing William Fuller V and selecting Jaylen Waddle in the first round of the draft. The former averaged 16.6 yards per catch with the Houston Texans in 2020. The latter averaged 18.9 yards per reception in college and already has familiarity with Tagovailoa thanks to their time together at Alabama. They will join wideout DeVante Parker and tight end Mike Gesicki in a solid pass-catching group.

On the first day of Dolphins mandatory minicamp, in a heavy downpour, Tagovailoa threw five interceptions, but that isn't a reason to panic so early in the offseason.

Typically, teams work through the wrinkles in an offense to find out what's effective or ineffective during spring practices, and Tagovailoa had a much better showing Wednesday.

Barring absolute face-plant performances within the first few weeks of the season, Tagovailoa shouldn't have to worry about the coaching staff benching him for Jacoby Brissett. The Dolphins have to find out what they have in Tagovailoa, but the team must exercise some patience.

Tagovailoa will learn a new system under co-offensive coordinators George Godsey and Eric Studesville, and he'll play with two new primary wideouts. Because of that, the 23-year-old signal-caller could have some early growing pains, which is why he's fifth in these rankings.

4. Baker Mayfield, Cleveland Browns

Baker Mayfield put together an efficient 2020 season, though he didn't do enough to escape the game-manager label.

Mayfield threw for 3,563 yards, 26 touchdowns and eight interceptions for a passing offense that ranked 28th in attempts and 24th in yards. Meanwhile, the Cleveland Browns ground attacked listed fourth in total carries with the third-most yards.

The Browns will likely continue to feed running backs Nick Chubb and Kareem Hunt, but wideout Odell Beckham Jr.'s return could open up the passing game with big plays over the top and yards after the catch. 

Last October, Beckham tore his ACL, but he's on the road to recovery. Fellow wideout Jarvis Landry said the three-time Pro Bowler looked "amazing" during a recent workout.

If the Browns finally see a glimpse of the playmaker who eclipsed 1,300 receiving yards in three consecutive terms with the New York Giants, Mayfield would have a good chance to top 4,000 yards and 30 touchdowns for the first time in his career.

Aside from Beckham and Landry, Mayfield also has a solid tight end duo in two-time Pro Bowler Austin Hooper and David Njoku.

Behind one of the league's top offensive lines and with a strong ground attack, Mayfield will have opportunities to rack up yards and touchdowns through the air in a more dynamic offensive attack.

Already settled in an offensive system, Mayfield takes the No. 4 spot over Tua Tagovailoa, who's an inexperienced starter working with first-time co-play-callers George Godsey and Eric Studesville.

3. Sam Darnold, Carolina Panthers

Sam Darnold will start a new chapter with the Carolina Panthers, who acquired him from the New York Jets. The USC product had an underwhelming three-year stretch with Gang Green, throwing for 45 touchdowns and 39 interceptions with a 59.8 percent completion rate.

The Jets deserve some criticism for Darnold's early shortcomings. As a rookie, he played under a defensive-minded head coach in Todd Bowles and offensive coordinator Jeremy Bates, who hadn't called plays since 2010.

Gang Green fired Bowles' staff after Darnold's rookie season and hired ex-head coach Adam Gase, whose offenses trended in the wrong direction during his three-year tenure with the Miami Dolphins.

In Carolina, Darnold will work with offensive play-caller Joe Brady, who coordinated the passing attack for LSU's 2019 championship team, which averaged the second-most yards (401.6) in the FBS. Last season in Carolina, Brady fielded a unit that featured a pair of 1,000-plus-yard receivers in DJ Moore and Robby Anderson.

Moore and Anderson can beat defenders with speed. The former averages 15.2 yards per reception. If Christian McCaffrey can stay healthy, he's a viable threat out of the backfield. The dual-threat running back recorded 116 catches for 1,005 yards and four touchdowns in 2019, but he missed 13 games last season.

Anderson played with Darnold for two seasons in New York and saw something different in the 24-year-old signal-caller, per The Athletic's Joseph Person.

"When I walked in the building, I see like a new energy out of him, like a glowing charisma that I didn't really see in New York," Anderson said. "You know when a person, when you can see a glow in them—their energy, their aura. I could kinda view that when I walked in the building, just being around him."

Darnold could cruise to career numbers with his core group of pass-catchers. He takes the No. 3 spot over Baker Mayfield, who has a lower ceiling in a run-dominant offense with two featured backs.

2. Daniel Jones, New York Giants

In his rookie season, Daniel Jones showed early flashes. Three weeks into the campaign, he took over for Eli Manning and finished with 24 touchdowns and 12 interceptions.

Last season, the New York Giants offense scored the second-fewest points in the league. The unit sorely missed running back Saquon Barkley, who missed 14 games with a torn ACL, but Jones struggled to move the ball through the air. He threw for 11 touchdowns and 10 interceptions. 

Even in a limited role, Barkley's presence may draw an extra defender in the box, which would open up the passing game. He can also catch out of the backfield.

Nonetheless, Jones' on-field connection with wideout Kenny Golladay will make or break the aerial attack. The two have made an effort to establish some chemistry through the spring, per The Athletic's Dan Duggan. 

"The Giants are counting on the addition of Golladay to help Jones make a leap in his third season," Duggan wrote. "The relationship is in its very early stages, but the first impression was promising."

With the Detroit Lions, Golladay became quarterback Matthew Stafford's go-to option while Marvin Jones Jr. and Golden Tate battled injuries during the 2018 campaign. He followed up with 1,190 receiving yards and a league-leading 11 touchdown receptions in 2019. 

Golladay isn't a silky-smooth route-runner, but he's going to haul in some acrobatic passes with his wide catch radius. Darius Slayton, Sterling Shepard and rookie first-rounder Kadarius Toney will round out a high-end wide receiver group.

If tight end Evan Engram can stay healthy, Jones would have another big-bodied target (6'3", 240 lbs) for third-down and red-zone situations. Thus far, he's missed 14 contests in four seasons.

Jones' stacked pass-catching group gives him the edge over Sam Darnold, who doesn't have a proven tight end or a clear-cut primary slot receiver following Curtis Samuel's departure.

1. Joe Burrow, Cincinnati Bengals

Joe Burrow saw his rookie campaign cut short with a torn ACL and MCL in Week 11 against the Washington Football Team. However, he expects to make a full recovery in the near future, per ESPN's Ben Baby.

"The knee still has a little ways to go, but my upper body, my right leg, everything else feels better than it ever has before," Burrow said. "When I'm on the field and executing, I'm playing better than I ever have before. So I'll continue the program we were on and get back to 100% before camp."

According to Dr. Neal ElAttrache (h/t ESPN Adam Schefter), Burrow is "all systems go" for the season opener against the Minnesota Vikings.

The Bengals have a top-tier wide receiver unit that features Tyler Boyd, Tee Higgins and rookie first-rounder Ja'Marr Chase.

Boyd has eclipsed 1,000 receiving yards in two seasons. Last year, Higgins recorded two 100-yard performances with Burrow under center and finished with a team-leading 908 yards and six touchdowns. Chase won the 2019 Fred Biletnikoff Award as a sophomore and established a rapport with the Bengals quarterback during a national title run that year.

Burrow will also have the option to dump off passes to running back Joe Mixon, who missed 10 games with a foot injury in 2020. He's a decent pass-catcher out of the backfield with 129 receptions for 1,008 yards and five touchdowns in 50 games.

Without much concern for Burrow's recovery, he edges Daniel Jones, who needs to build a rapport with his top wide receiver in Kenny Golladay. New York offensive coordinator Jason Garrett also has to find a way to utilize versatile wideout Kadarius Toney, who's already missed significant practice time.

Burrow knows the Bengals' system, and he's familiar with his top three wide receivers, which may result in eye-popping passing numbers for the 2021 season.