• K-means clustering groups together similar units: The algorithm created four groups based on 2023 defensive performance.

• Cluster 2 contains the NFL’s best-performing defenses: The Baltimore Ravens, Cleveland Browns, New York Jets and San Francisco 49ers headline the group.

• Get a head start on fantasy football: Use PFF’s fantasy football mock draft simulator to create real live mock draft simulations to get ready for your live draft!

Estimated Reading Time: 7 minutes

We can better understand how NFL defenses performed in 2023, and how they may stack up in 2024, by clustering them using PFF grades and metrics from this past regular season. PFF has in previous years performed clustering on wide receivers and quarterbacks, and we most recently looked at clustering offenses.

Clustering is a mathematical technique used to group similar observations. The most common form is the k-means clustering algorithm, which completes its iterative process when each observation is in the cluster that best represents it. In other words, there is no other cluster whose center (or mean of all the variables) is closer to that observation than the one it currently belongs to.

The graphic below shows the clusters formed by the algorithm and how similar NFL defenses are based on the two most important variables (called components).

Cluster 1

This cluster is made up of the lowest-graded defenses on average (62.36) and those with the highest average EPA allowed per play (0.13) when pass rushing. These teams allowed the highest average first-down conversion rate (30%) and blitzed the least (24.3%) of the clusters.

• Arizona Cardinals: The Cardinals earned the lowest defensive grade (54.7) in the NFL in 2023. They still ranked eighth in fourth-down conversion rate allowed (46.6%).

• Tennessee Titans: The Titans’ defense struggled in 2023, ranking 29th in defensive grade (67.9). They placed ninth, however, in first-down conversion rate allowed (27.3%).

• Washington Commanders: The Commanders rushed the passer the least often of any defense in 2023 (29.3%).

Cluster 2

Cluster 2 is made up of the highest-graded defenses (86.5) on average in 2023. These units featured the league’s best pass-rushers, culminating in an 82.5 average PFF pass-rushing grade. They also allowed the lowest average fourth-down conversion rate (46.1%).

• Baltimore Ravens: The Ravens’ defense ranked third in the NFL last season with a 90.5 grade. Their pass-rush unit won more than 50% of its pass-rush reps and earned the seventh-best grade.

• Buffalo Bills: The Bills’ run defense struggled in 2023, placing 27th with a 57.3 PFF grade. They ranked 13th in first-down conversion rate allowed (28%).

• Cleveland Browns: Cleveland was home to the highest pass-rush win rate of any team in 2023 (60.3%), and the defense allowed the lowest EPA per play on pass rushes (-0.27). They also allowed the lowest first-down conversion rate in the NFL (22.6%).

• Dallas Cowboys: The Cowboys posted the second-best pass-rush grade (90.6) in 2023. They produced pressure the most often of any team (44%) but ranked sixth in EPA allowed per play (-0.09).

• Kansas City Chiefs: The Chiefs did not provide their opponents many opportunities to convert to a new set of downs in 2023, ranking seventh in conversion rate allowed (26.9%). They pressured often (37.5%, 10th) and allowed the third-lowest EPA per play (-0.16) when doing so.

• Miami Dolphins: The Dolphins placed third in pressure rate (41.4%) last season. Their pass-rush unit ranked fifth with an 86.4 grade, but the defense as a whole allowed teams to convert to a new set of downs often (28%, 14th).

• New Orleans Saints: The Saints’ coverage unit earned a sixth-ranked grade in 2023 (91.2). They played Cover 1 often (32.2%), ranking second behind the Browns. They also ranked second in fourth-down conversion rate allowed (42.3%).

• New York Jets: The Jets fielded the NFL’s highest-graded defense in 2023 (90.8). They also boasted the top-ranked coverage unit (94.8) and allowed the second-lowest first-down conversion rate (24.9%).

• Pittsburgh Steelers: The Steelers constructed one of the highest-graded pass-rushing units in the league last season (88.8). They limited opposing offenses, allowing them to convert to a new set of downs at a low 26.5% clip, which ranked sixth.

• San Francisco 49ers: The 49ers tied with the Jets for the highest-graded defense in 2023 (90.8). Their run-defense and pass-rush units placed 10th and fourth, respectively, in PFF grade. The defense also ranked fourth in pass-rush win rate (55.7%).

Cluster 3

The defenses in Cluster 3 were known for strong run defense but mediocre efforts overall en route to an average 76.8 PFF grade. They played Cover 3 the most often of any cluster (33%).

• Carolina Panthers: The Panthers’ coverage unit placed ninth in PFF grade (88.4) last season. They put very little pressure on their opponents, ranking 31st with a 29.4% pressure rate. Carolina also allowed opponents to convert fourth downs at a 70% rate.

• Chicago Bears: The Bears ranked only 29th in pressure rate (31.1%) last season, and the unit won only 35.8% of its reps, ranking 31st.

• Cincinnati Bengals: The Bengals’ 68.9 defensive grade in 2023 ranked 28th in the NFL, and their coverage unit placed only 30th (61.4).

• Denver Broncos: The Broncos fielded one of the worst defenses in the league last season, slotting in at 31st with a 62.4 PFF grade. Their coverage unit finished last (53.3), but they did allow the second-lowest conversion rate on third downs (33.5%).

• Detroit Lions: The Lions’ run defense graded in the top 10 last season (75.5) and placed 11th in EPA allowed per play (-0.11). They struggled in coverage, however, ranking 28th with a 65.1 grade. They allowed opponents to convert fourth downs to a new set of downs at a 27th-ranked clip, too.

• Green Bay Packers: The Packers fielded an average defense in 2023, ranking 20th in PFF grade (74.0). They didn’t let their opponents convert fourth downs too often (46.7%, 10th).

• Houston Texans: The Texans had a decent run defense last season, placing 16th in PFF grade and allowing a seventh-ranked EPA per play of -0.12. Their coverage unit ranked seventh with a 90.3 grade. Houston’s weak link was allowing opponents to convert fourth downs, which they did at a 24th-ranked clip.

• Indianapolis Colts: The Colts’ defense was average in 2023, except their pass rush, which ranked 10th. They won 50% of their pass rushes (ninth best).

• Jacksonville Jaguars: The Jaguars struggled to get to opposing quarterbacks in 2023 on their way to a 63.8 PFF pass-rushing grade (28th). They did well to not allow opponents to convert on third down, ranking seventh.

• Las Vegas Raiders: The Raiders allowed their opponents to convert third downs at a high rate (42.1%, 28th) in 2023, and their run defense ranked sixth with a 73.6 grade.

• Los Angeles Chargers: The Chargers’ pass rush unit ranked 20th with a 71.8 grade in 2023. Their run defense stood out on its way to a 12th-ranked 66.2 grade. What hurt them the most was allowing fourth downs to be converted at a high rate, almost 60%.

No team played Cover 6 more than Los Angeles (24.4%).

• Los Angeles Rams: The Rams’ defense performed well in 2023, ranking ninth with a 69.1 PFF grade. Their coverage unit struggled, however, en route to a 58.2 grade to rank 31st.

• New York Giants: The Giants generated a 31.1% pressure rate in 2023, ranking only 28th. Their pass rush won just 36.3% of its reps, ranking 30th. Their run-defense unit didn’t fare much better, earning a 29th-ranked 56.2 grade.

• Philadelphia Eagles: The Eagles’ pass-rush and run-defense units were solid in 2023, ranking seventh and fourth, respectively. Despite this, they allowed one of the worst EPA per play figures on run defense (0.003). They also struggled in coverage, placing 23rd in PFF grade (72.5). Philadelphia also surrendered a high first-down conversion rate of 30.5%, ranking 29th.

• Seattle Seahawks: The Seahawks’ run defense struggled in 2023, allowing the highest EPA per play (0.03). They ranked 23rd in run-defense grade (59.6).

• Tampa Bay Buccaneers: The Buccaneers’ defense ranked 24th in grade in 2023 (71.3). They were also 24th in first-down conversion rate allowed (29.6%). Their run defense was more successful, allowing -0.16 EPA per play, which ranked third.

Cluster 4

The defenses in Cluster 4 excelled in run defense, averaging a 76.8 PFF grade. However, they allowed the highest average fourth-down conversion rate (57.5%).

• Atlanta Falcons: The Falcon’s run defense ranked second to the Dolphins with an 87.1 grade. Their pass-rush unit was not as successful, however, winning only 36.8% of their rushes, ranking 28th.

• Minnesota Vikings: The Vikings played Cover 0 at the highest rate in the NFL (12.1%) and also blitzed at the highest clip (58.3%). They did not come out on top on many of their rushes, though, ranking 24th in win rate (39.9%).

• New England Patriots: The Patriots won only 34.6% of their pass-rush reps in 2023, the lowest rate in the league. Their run defense was on the other end of the spectrum, allowing the lowest EPA per play (-0.19) in the NFL.