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The NFL's scoring average has hovered around 19-21 points for the better part of the Super Bowl era, but that number has ballooned this season to 24.2, which would be an all-time record if it stands.

Playing defense is harder than ever due to numerous factors, including offense-friendly rule changes, innovative offenses and rocket-armed quarterbacks. However, a few teams still have solid defenses.

Below, we'll rank the NFL's top 10 defenses based on the following factors.

Football Outsiders Defense-Adjusted Value Over Average (DVOA)

A proprietary Football Outsiders statistic, DVOA "measures a team's efficiency by comparing success on every play to a league average based on situation and opponent." The statistic is arguably the best analytical measurement of team success.

Interceptions and Forced Fumbles

Does the defense make game-altering plays?

We're counting forced fumbles (rather than recovered fumbles) here, as the former is a better measurement of a team's takeaway skills while the latter is based off odd bounces and ricochets.

Variance 

Separate from DVOA, Football Outsiders also ranks variance, which is "a measure of a team's game-to-game consistency as judged by total DVOA rating for each game." Defenses with less variance give their teams a better chance to win on a week-to-week basis. 

Notable Injuries and Personnel Changes 

The relative health of team defenses came into consideration, as did personnel changes or increased playing time for great players. For example, Dallas Cowboys linebacker Sean Lee has played in only four of his team's seven games, but he's back and should give the team a boost down the stretch. 

Coaching

Does the team's defensive coordinator have an impressive track record? If so, that helps the unit. 

Team Offense

If a team's offense underperforms, then the defense must work suboptimal circumstances, as it's on the field a lot and is forced to lead the team to victory. Defenses under more pressure in a given week to produce receive more credit here.

Overall

We'll throw everything together and come up with a ranking.  

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Football Outsiders DVOA: No. 14 overall (No. 9 vs. pass, No. 22 vs. run)

Interceptions and Forced Fumbles: T-16 in interceptions (six), T-4 in forced fumbles (11)

Variance: No. 7

Notable Injuries/Personnel Changes

Starting cornerback Quinton Dunbar has missed the past two games with a shin injury. He has no timetable for a return but he isn't on injured reserve, so he could make it back eventually.

Defensive lineman Matthew Ioannidis may have earned more playing time with a 2.5-sack performance against the New York Giants on Sunday. He's made three starts this year and has 5.5 sacks overall.

Coaching

Defensive coordinator Greg Manusky has a spotty track record in 11 years in that role with four different teams. Until this year, he never led a top-10 unit in fewest yards allowed per game. However, Manusky is excelling this season, as Washington is currently fifth in fewest yards allowed per play and tied for ninth in takeaways.

Team Offense

The Redskins are currently third in the NFL in time of possession. Adrian Peterson is leading the way with 587 yards and four touchdowns on the ground, although he's getting plenty of help from one of the league's best offensive lines.

Overall

Aside from the ugly 43-19 loss to the New Orleans Saints in Week 5, the Redskins have held every other opponent to no more than 21 points. They also gave up only 17 each to the Carolina Panthers and Green Bay Packers.

The ball-control offense is a big help, but Washington's defensive front is also young and has plenty of room to grow. Ioannidis is 24, while 2018 first-round nose tackle Da'Ron Payne is 21 and 2017 first-round defensive end Jonathan Allen is 23.

Safety D.J. Swearinger has also turned into a ballhawk, as he's picked off four passes in seven games.

While Washington's defensive metrics aren't elite, the team is getting it done on the field and forcing takeaways. It's impossible to keep the Redskins out of the top 10.

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Football Outsiders DVOA: No. 11 overall (No. 24 vs. pass, No. 4 vs. run)            

Interceptions and Forced Fumbles: T-29 in interceptions (two), T-21 in forced fumbles (five)          

Variance: No. 6

Notable Injuries/Personnel Changes

Linebacker Sean Lee has missed three games with a hamstring injury but is back healthy. Rookie linebacker Leighton Vander Esch shined in his place and is now second on the team in tackles, which helps Dallas' tremendous front-seven depth.

Strong safety Xavier Woods missed the first two games but has since returned.

Coaching

Defensive coordinator Rod Marinelli has been coaching in some capacity since 1973. His three-year stint as the Detroit Lions head coach didn't go well (the team went 10-38 during his tenure), but in his eight years as a defensive coordinator since then, his teams have never finished lower than 16th in fewest points allowed per game.

Team Offense

The Dallas offense has seen better days. Tight end Geoff Swaim is second on the team in receiving, and he has only 205 yards through seven games. As such, the defense has needed to hang tough in some back-and-forth slugfests.

The Cowboys' acquisition of Oakland Raiders wideout Amari Cooper may be beneficial, but good luck finding a No. 1 wideout with more week-to-week variance (he's had nine games with no more than two catches since Week 1 of 2017). Still, Cooper did lead off his career with two 1,000-yard seasons.

Overall

The Dallas front seven keeps the team in games in conjunction with star running back Ezekiel Elliott. Edge-rusher Demarcus Lawrence leads the team with 5.5 sacks, 23-year-old linebacker Jaylon Smith continues his triumphant return from a devastating injury with a team-leading 57 tackles and Lee and Vander Esch have been fantastic.

The Cowboys are a well-coached defense that hasn't allowed more than 24 points in any contest, and their young talent should only improve.

Rick Scuteri/Associated Press

Football Outsiders DVOA: No. 9 overall (No. 11 vs. pass, No. 13 vs. run)

Interceptions and Forced Fumbles: T-16 in interceptions (six), T-7 in forced fumbles (nine)

Variance: No. 4

Notable Injuries/Personnel Changes

Arizona Cardinals linebacker Markus Golden missed three games, but he is back and had a great Week 8 game versus the San Francisco 49ers (one sack, seven tackles). Safety Tre Boston has missed his past two games with shoulder and ribs injuries.

Coaching

Head coach Steve Wilks runs the show and brings over an impressive resume from his time with the Panthers as defensive backs coach and defensive coordinator. 

Al Holcomb, who worked with Wilks in Carolina for five years, is in his first year as a defensive coordinator. The two have brought over a 4-3 zone-based scheme after Arizona went with a 3-4 defense during the Bruce Arians era.

Team Offense

No team has held the ball less than the Cardinals, who rank last in time of possession at 25:14. For context, the next-closest team (the Cincinnati Bengals) is at 27:43. Arizona has already undergone a quarterback and offensive coordinator change, too.

In other words, the offense's lackluster performance has put Arizona's defense in a bind.

Overall

The defense is doing the best it can under adverse conditions, as the 2-6 Cardinals are playing out the string. Arizona is tied for sixth leaguewide in fewest yards per play allowed (5.3).

Shutdown cornerback Patrick Peterson is a three-time All-Pro who is one of the best at his position ever. Safety Budda Baker is only 22 and leads the team with 70 tackles. Edge-rusher Chandler Jones hasn't slowed down after leading the league in sacks in 2017, as he has 6.5 so far.

The defensive talent is clearly present, but it's difficult for them to overcome the significant offensive obstacles the team faces every week.

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Football Outsiders DVOA: No. 4 overall (No. 4 vs. pass, No. 12 vs. run)

Interceptions and Forced Fumbles: T-19 in interceptions (five), T-1 in forced fumbles (13)

Variance: No. 32

Notable Injuries/Personnel Changes

Defensive backs Micah Hyde and Phillip Gaines have missed a combined three games, although both are back. The defense has been mostly healthy otherwise.

Coaching

Leslie Frazier made his mark with an excellent resume as the Minnesota Vikings' defensive coordinator last decade, as his defenses ranked sixth in yards allowed per game in both 2008 and 2009.

A head-coaching stint in Minnesota wasn't as successful, but he's now been in the NFL for 20 years and has more experience than nearly anyone else running a defense.

He's been solid as the Bills' defensive coordinator under head coach Sean McDermott, who had plenty of success running a stout Panthers defense earlier this decade.

Team Offense

No team has scored fewer points than the Bills, who have now started three quarterbacks in two months. Buffalo is tied for fifth in the league in giveaways (16) and is second in interceptions (12). The Bills also haven't gained more than 303 yards in a game all season.

Like many of the other teams featured here, Buffalo's defense has to bring its best every week for the team to have a puncher's chance at winning.

Overall

The Bills have been feast or famine. They allowed 47 points to the Baltimore Ravens in Week 1 and 28 to the Los Angeles Chargers in the first half in Week 2. But from halftime of Week 2 through the end of Week 6, the Bills defense proceeded to give up only 56 points. Just as Buffalo appeared to be rolling defensively, it allowed 37 points to the Indianapolis Colts in Week 7.

It's been a bizarre year in Buffalo, especially with the team's significant offensive concerns. But the defensive future is bright with 20-year-old linebacker Tremaine Edmunds (54 tackles), second-year linebacker Matt Milano (46 tackles and three fumble recoveries) and 23-year-old shutdown cornerback Tre'Davious White.

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Football Outsiders DVOA: No. 5 overall (No. 14 vs. pass, No. 1 vs. run)

Interceptions and Forced Fumbles: T-14 in interceptions (seven), T-4 in forced fumbles (11)          

Variance: No. 18

Notable Injuries/Personnel Changes

Middle linebacker Zach Cunningham will be out for "at least a few weeks" with a knee injury, per Aaron Wilson of the Houston Chronicle. The second-year pro is leads the team in tackles with 62.

Houston has also endured an unusual amount of secondary injuries, with cornerbacks Kayvon Webster, Shareece Wright and Aaron Colvin all missing time. Webster is out for the year, but Wright and Colvin should return eventually.

On the plus side, rookie safety Justin Reid has entered the team's starting lineup for good after he largely came off the bench for the first month of the season. He's responded well with 17 tackles and an interception in his past three games. For the year, he has posted two picks (team co-leader) and 37 tackles (fifth on the team).

Coaching

Defensive coordinator Romeo Crennel is one of the best in the game. He was the New England Patriots' defensive coordinator when the team won three Super Bowls from 2001-2004.

Crennel didn't find much success in head coaching stints with the Cleveland Browns and Kansas City Chiefs, but he has been excellent since his arrival in Houston in 2015. His Texans teams have ranked third, first and ninth in yards allowed per game in his three seasons, respectively. 

Team Offense

The Houston offense has struggled for much of the year, as the offensive line has given up 26 sacks (tied for fourth in the league). The run game has been inconsistent, although Lamar Miller has come on strong in Weeks 7 and 8 (233 rushing yards and a pair of scores).

Quarterback Deshaun Watson is playing through a chest injury, but he looked great while throwing five touchdowns in a 42-23 win over the Miami Dolphins on Thursday. Perhaps the offense has turned a corner.

Overall

A defense with a healthy J.J. Watt will always be among the league's best. He's been tremendous with eight sacks, 30 tackles and four forced fumbles. Edge-rusher Jadeveon Clowney may be having his best season yet (4.5 sacks), and safety Tyrann Mathieu has been an excellent addition to the secondary (two picks, two sacks, 46 tackles).

If the offense consistently exhibits the form it showed Thursday, that will ease the pressure on the defense. That would only mean great things for Houston, which looks well on its way to an AFC South crown.

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Football Outsiders DVOA: No. 2 overall (No. 3 vs. pass, No. 6 vs. run)

Interceptions and Forced Fumbles: No. 5 in interceptions (10), No. 10 in forced fumbles (seven)

Variance: No. 23

Notable Injuries/Personnel Changes

All-Pro safety Earl Thomas suffered a broken leg in Week 4 and is out for the season. Linebacker Mychal Kendricks is suspended indefinitely for violating the league's personal conduct policy after he pled guilty to insider trading. Linebacker Bobby Wagner and cornerback Tre Flowers have each missed a game but are back.

Coaching

Defensive coordinator Ken Norton Jr. is in his first year leading the Seahawks after three seasons of running defenses for the Raiders. The ex-star linebacker didn't find much success in Oakland, as the team never finished higher than 22nd in fewest yards per game allowed under him. However, Norton has led an excellent unit this year and deserves credit for helping keep the team afloat despite Thomas' loss.

Team Offense

The resurgent run game has eased burdens on the defense. Of note, the Seahawks had the ball for nearly 35 minutes in their 28-14 win over the Lions on Sunday. Running back Chris Carson played a big role as he rushed for 105 yards on 25 carries. He leads a backfield that ranks fifth in rushing yards per game.

Overall

If you look at Seattle's 2018 performances, how many of them can you say were bad? A few so-so outings are mixed in with good ones, but the Seahawks haven't laid an egg. They did allow 33 points at home to the Los Angeles Rams, but that's around an average day at the office for that high-scoring team.

Seattle's hot defense has allowed more than 17 points just once since Week 2. The Seahawks secondary is also young, with three starters (Shaquill Griffin, Tre Flowers and Tedric Thompson) all 23 years old. Presumably, they will only get better as they learn and develop. Defensive end Frank Clark, who is 25 years old, leads the team with 6.5 sacks.

Everything is coming together at the right time, which makes Seattle a playoff dark horse.

Mark LoMoglio/Associated Press

Football Outsiders DVOA: No. 3 overall (No. 1 vs. pass, No. 27 vs. run)

Interceptions and Forced Fumbles: No. 1 in interceptions (12), No. 2 in forced fumbles (12)

Variance: No. 22

Notable Injuries/Personnel Changes

The loss of middle linebacker Joe Schobert to a hamstring injury has hindered the Browns defense.

Schobert suffered the setback during a 38-14 loss to the Chargers in Week 6. Including that contest, the Browns have allowed an average of 32.3 points per game in the past three weeks.

Schobert is still third on the team in tackles despite missing two full games. He has no timetable for a return but has not been put on injured reserve, so there is hope for a comeback.

Linebacker Christian Kirksey also missed two games with an ankle injury but is back. Cornerback Terrance Mitchell is on injured reserve with a broken forearm but is eligible to return in a month if he's healthy.

Coaching

Over his 20-year career as a head coach or defensive coordinator, Gregg Williams has overseen some excellent defenses (the 2000 Tennessee Titans) and some not-so-great defenses (last year's Browns). He's leading a hot one now, however.

Williams became the interim head coach after Hue Jackson and offensive coordinator Todd Haley were fired Monday, so don't expect anything to change on defense with that move.

Team Offense

The offense has put up more than 23 points just once. As noted before, the league average for points per game is 24.2, which makes the Browns' performance even worse. Cleveland is also a middling 13th in time of possession.

Overall

The Browns have been in constant turmoil since rejoining the league in 1999. They've made the playoffs once since then and perpetually have one of the worst teams in football.

That's the case this year, but it's not on the defense, which features some of the game's best young talent (defensive end Myles Garrett and cornerback Denzel Ward chief among them).

Cleveland's defensive future is bright and will be especially so when Schobert comes back. If the offense can turn it around with a coaching change, that should only help the defense.

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Football Outsiders DVOA: No. 8 overall (No. 8 vs. pass, No. 8 vs. run)

Interceptions and Forced Fumbles: No. 24 in interceptions (four), No. 31 in forced fumbles (two)

Variance: No. 8

Notable Injuries/Personnel Changes

There isn't much to speak of here, as the team has been largely healthy on defense. Starting cornerback A.J. Bouye did sit out Sunday's 24-18 loss to the Philadelphia Eagles with a calf injury. That was his first missed game of the year.

Coaching

Defensive coordinator Todd Wash took over in 2016 and immediately made an impact. The Jags were 24th in yards allowed per game in 2015, but Wash helped improve that mark to sixth in 2016 and then second in 2017 and 2018. He's been in the NFL for 12 seasons.

Team Offense

The Jaguars defense must bring it every week, given the offense's struggles. The Jags are tied for second-worst with 18 giveaways, and they rank 29th in points scored per game. On Football Outsiders, the Jags are No. 27 in offensive DVOA.

The good news is running back Leonard Fournette should return in two weeks, per Adam Schefter of ESPN.com, but how effective will he be after missing all but two games with a hamstring injury?

Overall

The Jags' season has been disappointing after a 3-5 start, but despite their lack of takeaways, the defense isn't to blame.

The Jaguars have a couple of performances they'd likely want back (such as the team's 40-7 loss to the Cowboys), but they also went into Kansas City (No. 1 in the NFL in scoring) and held the Chiefs to 23 points despite five turnovers from the offense.

Also, takeaway variance should swing in their direction. This is largely the same defense as last season, when the team ranked second in interceptions (21) and third in forced fumbles (17).

The two best offensive opponents they'll see all year (the Patriots and Chiefs) are behind them, so the schedule gets a little easier. Expect the Jags to stay a top-five unit at worst.

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Football Outsiders DVOA: No. 6 overall (No. 10 vs. pass, No. 5 vs. run)

Interceptions and Forced Fumbles: No. 19 in interceptions (five), No. 25 in forced fumbles (four)         

Variance: No. 28

Notable Injuries/Personnel Changes

Starting cornerback Marlon Humphrey, who was the team's first-round pick in 2017, has sat out the last two games (both losses) with a thigh injury. Starting corner Jimmy Smith was suspended for the first four contests for violating the NFL's personal conduct policy.

Coaching

Defensive coordinator Don Martindale is in his first season in the role after taking over for Dean Pees, who is the leader of the Tennessee Titans defense.

Martindale has only been an NFL defensive coordinator once before (a forgettable 2010 season with the Denver Broncos when they allowed the most points per game in football), but he's received much praise for his work this year, and veteran safety Eric Weddle gave his coordinator credit for being "a step ahead" of the Pittsburgh Steelers in a crucial 26-14 road win.

Team Offense

The Ravens only have two defensive performances to regret (a 34-23 loss to the Bengals and a 36-21 defeat against the Panthers). However, the Ravens also committed three turnovers in each game, which presented the opposition with some shorter fields. The defense didn't play well either time, but the offensive performance didn't help.

The Ravens offense is productive enough to give its defense some rest (Baltimore is sixth in time of possession).

Overall

Yes, the Ravens just disappointed in the aforementioned loss to Carolina sans Humphrey, but the key is to look at the overall season. In that case, we see some excellent performances, including a 21-0 victory at the Titans where they sacked quarterback Marcus Mariota 11 times (the team leads the league with 27 overall).

Baltimore has held five of its eight opponents to 14 or fewer points, but one of its best defensive days may have come against the New Orleans Saints in a 24-23 loss. New Orleans has one of the league's best offenses, but Baltimore held the Saints to seven points through three-plus quarters. New Orleans broke through with 17 in the fourth, although the Saints had 50.9 fewer yards than their season average on the day.

Baltimore can hang with any offense, and when Humphrey returns, the unit should only get stronger.

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Football Outsiders DVOA: No. 1 overall (No. 5 vs. pass, No. 3 vs. run)

Interceptions and Forced Fumbles: No. 2 in interceptions (11), No. 3 in forced fumbles (11)

Variance: No. 9

Notable Injuries/Personnel Changes

Star edge-rusher Khalil Mack (five sacks in six games) injured his ankle in the first quarter of a Week 6 battle at the Dolphins and was limited in Week 7 vs. the Patriots. He sat for the team's Sunday win vs. the New York Jets to recuperate. 

Elsewhere, rookie linebacker Roquan Smith (second on team in tackles) sat most of Week 1 loss to the Packers before entering the starting lineup in Week 2. He's been a mainstay since.

Coaching

Defensive coordinator Vic Fangio is one of a best at his role (if not the best). He led the 49ers defense to top-five performances in fewest yards and points allowed per game from 2011 to 2013 (if you include 2014, it was still top 10). Fangio is so good that new head coach Matt Nagy retained him after ex-lead man John Fox was fired following the 2017 campaign.

Team Offense

The Bears offense scored 63 points through three games (21 ppg), but they've been on fire ever since with an average of 32.8 points per contest in their past four. Chicago also ranks second in time of possession, so the offense has helped the defense stay fresh for the most part.

Overall

One could make a case for half of this list to be called the league's No. 1 defense, but the Bears get the slight nod.

The team's two worst defensive performances (31-28 loss to Miami, 38-31 defeat against New England) came while Mack was hurt. If he is back to 100 percent upon his return, the defense should consistently revert to its September form.

The Bears also make plays and provide their offense with a tremendous amount of support. Their week-to-week performances have been (mostly) consistent, and they're also the only team to hold the Tampa Bay Buccaneers to fewer than 26 points (Chicago won 48-10).

Chicago holds the No. 1 spot, although given how close the top defenses are in an offense-friendly NFL, that could change.