No player had a bigger breakout this season than Patrick Mahomes. The quarterback took over the starting job in Kansas City and exceeded all expectations, already throwing for more than 4,500 yards and 45 touchdowns.
There's only one Mahomes, but every team has a player, position group or coach who reached a whole new level this season. Our NFL Nation reporters have the NFL's biggest breakthroughs.
How we rank: Our power panel -- a group of more than 80 writers, editors and TV personalities -- evaluated how teams stack up through 15 weeks of the season.
Previous rankings: 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | Preseason
1. New Orleans Saints (12-2)
Week 15 ranking: 1
Biggest breakthrough: DT Sheldon Rankins. The 12th pick in the 2016 draft has been a solid starter throughout his career. But this season, he has really started to play at a Pro Bowl level, with eight sacks and 12 tackles for loss. He is a big part of the NFL's No. 1 run defense. Rankins (6-foot-2, 305 pounds) has always been a great athlete for his size, but he said he went back to using more of his power this season to set up that athleticism. -- Mike Triplett
2. Los Angeles Chargers (11-3)
Week 15 ranking: 4
Biggest breakthrough: WR Mike Williams. After a disappointing rookie season limited by injuries, the Clemson product is having a bounce-back year, leading the Chargers in receiving touchdowns with nine. Williams has totaled 37 receptions for 592 yards and helped lift the Bolts over the Kansas City Chiefs last week with a three-touchdown performance. -- Eric D. Williams
3. Kansas City Chiefs (11-3)
Week 15 ranking: 2
Biggest breakthrough: QB Patrick Mahomes. The Chiefs no longer have to go with some other team's castoff at the most important position, as they did for most of their first 58 seasons. With Mahomes at quarterback, the Chiefs have the look of a team that will contend for division and conference championships for years to come. -- Adam Teicher
4. Los Angeles Rams (11-3)
Week 15 ranking: 3
Biggest breakthrough: S John Johnson III. Johnson is a second-year pro whom the Rams drafted in the third round from Boston College. He made his way into the starting lineup five games into his rookie season, but in 2018, Johnson has taken his play to the next level. He has intercepted a team-best four passes, has 10 pass deflections and is second on the team in total tackles with 106. -- Lindsey Thiry
5. Chicago Bears (10-4)
Week 15 ranking: 6
Biggest breakthrough: QB Mitchell Trubisky. The second overall pick of the 2017 draft, Trubisky passed for only 2,193 yards, seven touchdowns and seven interceptions last season as a rookie. But Trubisky is having a breakout second season, with 2,814 passing yards, 23 touchdowns, 12 interceptions and three rushing touchdowns in 12 appearances so far. Trubisky is flourishing thanks to improved talent at the Bears' skill positions and the coaching of Matt Nagy, who brought Andy Reid's highly successful Kansas City offense with him to Chicago. -- Jeff Dickerson
6. Houston Texans (10-4)
Week 15 ranking: 7
Biggest breakthrough: DE Christian Covington. He has exploded for 3.5 sacks the past four games after totaling 4.0 in his first three NFL seasons. In his fourth season out of Rice, the 2015 sixth-round pick is quietly having his best season on a defense loaded with stars. Covington's best game came in Week 12 on Monday Night Football, when he recorded 2.5 sacks in a 34-17 victory against Tennessee. -- ESPN
7. New England Patriots (9-5)
Week 15 ranking: 5
Biggest breakthrough: CB J.C. Jackson. The undrafted rookie out of Maryland made the 53-man roster out of training camp and is playing meaningful snaps in some of the team's most important games -- and holding up well. Could this be a Malcolm Butler-type story? It's early yet, but Jackson has flashed confidence, ball skills and fluid movement skills while showing that the NFL stage isn't too big for him. -- Mike Reiss
8. Pittsburgh Steelers (8-5-1)
Week 15 ranking: 10
Biggest breakthrough: WR JuJu Smith-Schuster. Linebacker T.J. Watt is also deserving for his 11 sacks in his second season, but Smith-Schuster's star turn is hard to ignore. He isn't a supporting player to Antonio Brown. He's a marquee player alongside Brown after registering 95 catches, 1,274 yards and six touchdowns through 14 games. He has a flair for the big play, Ben Roethlisberger loves throwing to him, and he hasn't caught fewer than three passes in a game this season. -- Jeremy Fowler
9. Indianapolis Colts (8-6)
Week 15 ranking: 12
Biggest breakthrough: Offensive line. Finally. The line has gone from being a weak link during the first six years of Andrew Luck's career to being a strength of the Colts this season. That group has given up only 16 sacks, second fewest in the NFL, after giving up a league-high 56 last season. Improved line play has played a significant factor in helping the Colts to a top-10 total and scoring offense. -- Mike Wells
10. Baltimore Ravens (8-6)
Week 15 ranking: 11
Biggest breakthrough: RB Gus Edwards. The undrafted rookie went from being on the practice squad for the first five weeks of the season to being the NFL's fourth-leading rusher the past five games. Only Saquon Barkley, Derrick Henry and Ezekiel Elliott have produced more rushing yards than Edwards since Week 11. Edwards' physical running style inside the tackles complements Lamar Jackson's speed to hit the edges. Edwards has filled the void left by Alex Collins, whose disappointing season ended with him going on injured reserve earlier this month. -- Jamison Hensley
11. Seattle Seahawks (8-6)
Week 15 ranking: 9
Biggest breakthrough: RB Chris Carson. He looked like he was about to break out as a rookie seventh-round pick last season, when he beat veterans Eddie Lacy and Thomas Rawls for the starting job, only to land on injured reserve for good after the fourth game. It's happening now instead. Carson has held off first-rounder Rashaad Penny for the lead role in Seattle's backfield, and his career-best 119 yards on Sunday put him 87 away from 1,000, a mark no Seattle running back has reached since Marshawn Lynch in 2014. Carson is eighth in the NFL with an average of 2.3 yards after contact per rush. That rugged running style helped him score a third-effort touchdown in Seattle's loss to San Francisco on Sunday. -- Brady Henderson
12. Dallas Cowboys (8-6)
Week 15 ranking: 8
Biggest breakthrough: The defense. Yes, the group was listless in a 23-0 loss to the Colts on Sunday, but when judged over the course of the season, the answer is obvious. The Cowboys have had a defense the past few seasons that has been better than people think. They finished eighth in total yards in 2017. They led the league in rushing defense in 2016. They took the ball away 31 times in 2014. This season, however, they have been elite, ranking fourth in points allowed and fifth in yards per game. They have one of the premier pass-rushers in DeMarcus Lawrence, two of the top young linebackers in Jaylon Smith and Leighton Vander Esch, and Byron Jones has been the Cowboys' best cornerback in years after making the transition back from safety. -- Todd Archer
13. Minnesota Vikings (7-6-1)
Week 15 ranking: 13
Biggest breakthrough: The running game. Mike Zimmer said it best: When Dalvin Cook has the ball in his hands, good things typically happen for the Vikings' offense. After weeks of struggling to generate a potent rushing attack, Minnesota keyed in on the 31st-ranked run defense and ran circles around Miami, notching season highs in attempts (40), yards (220) and rushing touchdowns (three). The way Cook affected the game helped set up a potent play-action attack for Kirk Cousins and stymied the issues that were causing the Vikings to fall short in three recent losses. -- Courtney Cronin
14. Tennessee Titans (8-6)
Week 15 ranking: 14
Biggest breakthrough: LB Jayon Brown. He was primarily a substitution-package player as a rookie in 2017. His playing time has gotten a heavy boost this season, and he has become one of the best players on defense. Brown worked with former UCLA teammate and current Packers defensive lineman Kenny Clark and spent some time with Packers linebacker Clay Matthews during the offseason. He credits his work with them as a reason for a renewed, more aggressive mindset. Brown has 79 tackles (eight for a loss), 10 quarterback hits and six sacks. -- Turron Davenport
Stephen A. Smith explains why Aaron Rodgers should still be considered one of the best quarterbacks of all time despite the Packers' struggles this season.
15. Philadelphia Eagles (7-7)
Week 15 ranking: 15
Biggest breakthrough: RB Wendell Smallwood. The third-year pro had a pair of touchdowns in the team's biggest victory of the season against the Rams on Sunday. On the roster's fringe heading into 2018, he has made the most of his opportunity since injuries hit the position. -- Tim McManus
16. Carolina Panthers (6-8)
Week 15 ranking: 16
Biggest breakthrough: RB Christian McCaffrey. While McCaffrey led the Panthers with 80 catches in 2017, he wasn't the complete back he has become this season since the release of Jonathan Stewart. McCaffrey has gone from 3.7 yards rushing per carry to 5.2 this season. He entered Monday night's game with 926 yards rushing after having 435 last season. -- David Newton
17. Cleveland Browns (6-7-1)
Week 15 ranking: 20
Biggest breakthrough: Offensive coordinator Freddie Kitchens. Kitchens has unlocked Baker Mayfield and the Browns' offense since taking over as coordinator after eight games. Kitchens has adeptly called plays, using creative calls and formations to energize Nick Chubb, Mayfield and the offense. With Todd Haley and Hue Jackson, Mayfield was sacked 20 times and averaged 6.6 yards per pass. With Kitchens, Mayfield has been sacked five times and averaged 8.7 per pass. To think that most asked, "Who?" when Kitchens was made coordinator. -- Pat McManamon
18. Miami Dolphins (7-7)
Week 15 ranking: 17
Biggest breakthrough: CB Xavien Howard. He began to emerge in the second half of the 2017 season, but he exceeded even the highest of expectations with what he has been able to do in 2018. Howard is tied for the NFL lead with seven interceptions, despite playing just 12 games, and he's forcing people to count his name among the NFL's top young cornerbacks. Howard's instincts and ball skills have always been there, but his true breakthrough has been his understanding of offensive schemes and his baiting quarterbacks into making poor decisions. He has become arguably the Dolphins' best player. -- Cameron Wolfe
19. Green Bay Packers (5-8-1)
Week 15 ranking: 19
Biggest breakthrough: RB Aaron Jones. Just think what kind of numbers he could have put up had he not been suspended for the first two games and had the Packers not been so hesitant to commit to him as their full-time guy. The second-year pro leads all qualifying running backs with a 5.5-yard average. He has eight rushing touchdowns in 11 full games (he dropped out of Sunday's game against the Bears with a knee injury after just four carries). His 16-game projection would have him at just more than 1,000 yards. Instead, he'll probably end up at 728 yards this season if he misses the final two games, but he has given the Packers a clear-cut No. 1 back heading into next season. -- Rob Demovsky
20. Denver Broncos (6-8)
Week 15 ranking: 18
Biggest breakthrough: RB Phillip Lindsay. Lindsay, signed as an undrafted rookie free agent, has seen his production dip in recent weeks, but the (Denver) South High School graduate has been the hub of the Broncos' offense since the first week of the season and is fifth in the league in rushing. Honorable mention goes to LB Bradley Chubb, who as the No. 5 pick of the draft was expected to be an impact player, but he has likely exceeded the Broncos' high hopes for him. He has 12 sacks, has been a consistent performer in run defense and showed every bit of the level-headed maturity the Broncos thought he had before the draft. As linebacker Von Miller put it: "Chubb? The sky is the limit for him. He can do it all.'' -- Jeff Legwold
21. Washington Redskins (7-7)
Week 15 ranking: 21
Biggest breakthrough: The defensive line. Three players could be considered breakout guys up front: ends Matt Ioannidis and Jonathan Allen and nose tackle Daron Payne. The Redskins' defense has been sliding for most of the second half of the season, but this group continues to produce. These players have shown a little wear and tear at times because of heavy usage, but overall, they continue to make plays and take on double-teams. But they also pressure the passer. Ioannidis is second on the Redskins with 7.5 sacks; Allen is third with seven, and Payne has five -- but is second in tackles for loss with 9.5. The Redskins have their issues, but they also have three linemen with less than three years' experience to build around. -- John Keim
22. Atlanta Falcons (5-9)
Week 15 ranking: 23
Biggest breakthrough: DB Damontae Kazee. He is tied for second in the league with six interceptions. Kazee did not have an interception in 156 snaps last season; he has played six times as many snaps this season after replacing the injured Ricardo Allen (Achilles) at free safety. Coach Dan Quinn said he sees Kazee's future at either safety or nickelback. -- Vaughn McClure
23. New York Giants (5-9)
Week 15 ranking: 22
Biggest breakthrough: The Giants' rookie class. It has been a promising season for general manager Dave Gettleman's first draft class. First-round pick Saquon Barkley has been one of the best running backs in football. Second-round pick Will Hernandez has been a plug-and-play guard. Third-round pick B.J. Hill leads the team in sacks (5.0), and outside linebacker Lorenzo Carter has flashed talent. All in all, the rookies' production is one of the few bright spots in another losing season. -- Jordan Raanan
24. Tampa Bay Buccaneers (5-9)
Week 15 ranking: 24
Biggest breakthrough: DE Jason Pierre-Paul. While he has reached the Pro Bowl twice and amassed 70 career sacks, 2018 marks the first time that he has reached double-digit sacks since he suffered a catastrophic hand injury in a fireworks accident in 2015 -- an accident that threatened not only his career but also his life. His 11.5 sacks through 14 games this season are eighth among defensive linemen and mark the first time a Bucs player has reached double-digit sacks in a season since Simeon Rice in 2005. That was the NFL's longest team double-digit sack drought. Rice, who had 122 in his career, told ESPN of Pierre-Paul, "Look at what he's been through. It's bigger than football. It's who he is in his core. The fabric of the man won't let him concede." -- Jenna Laine
25. Cincinnati Bengals (6-8)
Week 15 ranking: 27
Biggest breakthrough: DE Sam Hubbard. The rookie third-round pick has shown flashes at times as a rotational player, but he really shined against the Raiders with two sacks and a forced fumble. He has six sacks and now has his eye on Carlos Dunlap's rookie sacks record of 9.5 with two games left to get it. -- Katherine Terrell
26. Detroit Lions (5-9)
Week 15 ranking: 25
Biggest breakthrough: LB Jarrad Davis. He still has his issues -- pass coverage, for instance, is not a strength -- but the Lions have found a strong role for their 2017 first-round pick. He has developed immensely as a pass-rusher and should be a player Detroit can count on for at least the next two seasons. He's still a smart, instinctual player, and his ability to hit and read plays has continued to develop. Missed tackles remain a problem, but overall Davis has shown that he can be a good middle linebacker (and perhaps a better pass-rushing linebacker) at this level. -- Michael Rothstein
27. Buffalo Bills (5-9)
Week 15 ranking: 28
Biggest breakthrough: WR Robert Foster. He was a four-star recruit for Alabama in 2013 who caught only 35 passes for 389 yards in four disappointing seasons for the Crimson Tide. An undrafted rookie, he recorded his third 100-yard receiving game on Sunday for the Bills, and with 19 catches, Foster has more yards (468) in the NFL than he did in college. -- Mike Rodak
28. Jacksonville Jaguars (4-10)
Week 15 ranking: 26
Biggest breakthrough: WR Dede Westbrook. He missed more than half his rookie season with a sports hernia, but he has become the Jaguars' best and most dependable receiver in 2018. He leads the team in catches, receiving yards and receiving TDs, and he returned a punt 74 yards for a touchdown Sunday. He's pretty much the Jaguars' only edge playmaker, and he has scored the team's only two touchdowns the past three weeks. Westbrook needs to be a bigger part of the offense the rest of this season and beyond. -- Mike DiRocco
29. San Francisco 49ers (4-10)
Week 15 ranking: 30
Biggest breakthrough: TE George Kittle. The 49ers believed strongly that he could be a difference-maker after he fell into their laps in the fifth round of last year's draft. Kittle flashed that potential in 2017, but injuries slowed him from having the type of splashy rookie season that would draw much national attention. Now healthy, Kittle has had a breakthrough season that has vaulted him into the upper echelon of the league's tight ends. He already has set the 49ers' franchise record for receiving yards by a tight end in a season and is within striking distance of the NFL record (1,327 yards). As a bonus, he is also an excellent blocker and is entrenched as a key component of the franchise. -- Nick Wagoner
30. New York Jets (4-10)
Week 15 ranking: 29
Biggest breakthrough: DE Henry Anderson. He has six sacks, twice as many as he did in his three-year total with the Colts. The Jets traded a seventh-round pick for Anderson during the draft, thinking he'd be a rotational player. He has exceeded expectations, and the timing couldn't be better. He will be an unrestricted free agent for the first time. -- Rich Cimini
31. Oakland Raiders (3-11)
Week 15 ranking: 31
Biggest breakthrough: TE Lee Smith. The eighth-year veteran entered 2018 with four career touchdown receptions, the most recent coming in 2015. After Sunday's score, Smith has three TDs in his past three games. Mere one-dimensional, blocking tight end? Well, that was certainly his rep, which is a major reason he has been so wide-open on his scores. "We'll keep featuring him in the passing game," QB Derek Carr said. "He's a good target, but the best thing that he does, besides being a great teammate, is his blocking. Any time we can get him the ball, it's a plus." -- Paul Gutierrez
32. Arizona Cardinals (3-11)
Week 15 ranking: 32
Biggest breakthrough: WR Christian Kirk. He might be just a rookie, but the second-rounder has had the biggest breakthrough of any Cardinal this season. When he broke his foot two weeks ago, Kirk was the Cardinals' leading receiver with 536 yards -- leading future Hall of Famer Larry Fitzgerald by 76 yards at the time. Kirk was expected to have a role in the offense, but he exceeded expectations during his 12 games. -- Josh Weinfuss