Week 7 EPA Power Rankings: Which NFL Defenses Stand Tall Through 6 weeks?

New England remains in control of the NFL, and might not be tested until the last third of the season.

There's an old adage in football that "defense wins championships."  The Super Bowl is filled with examples of this.  Last year the Patriots stymied a prolific Rams offense, holding them to just 3 points.  In 2013, the Broncos record-breaking offense was held to just 8 points when they were drubbed by the Seahawks.  Just two years later, a rebuilt version of that Broncos team carried what was left of Peyton Manning to a ring, holding the Panthers' highest-scoring offense to just 10 points.

Meanwhile, there's a newer adage in the analytical community of football that says "defense doesn't matter."  This is really just a hyperbolic way of saying defense is harder to predict than offense, it is partially driven by the offenses a team plays, and offense more reliably predicts team success.  It matters, but in a macro sense, it matters far less than offense.

Keeping that in mind, let's take a look at this week's EPA power ranks, where the most dominant defense happens to sit on top yet again.

(Reminder: Expected Points uses data from previous NFL seasons to determine how many points a team is likely to come away with on a given play, based on down, distance, time remaining, and field position. The difference in expected points at the start of a play and expected points at the end is referred to as expected points added, or EPA.)

Houston pops into the top-3 this week with a big win in Kansas City.  Their offense is starting to roll, and Deshaun Watson has moved into fourth in the NFL in EPA/dropback on the season.  Kansas City, meanwhile, dropped to their lowest spot of the year.  Hobbled offensive linemen, a starting wide receiver, and quarterback Patrick Mahomes are probably more to blame here though, and once they get healthy again that offense still looks as potent as ever.

The biggest riser this week is the Denver Broncos.  Pitching a shutout is a great way to do that.  The Broncos ran Marcus Mariota off the field after he was held to 3.5 Y/A to go along with two interceptions.  Ryan Tannehill was a bit more effective in relief, but still threw more interceptions than touchdowns.  The Saints also saw a good jump, moving up five spots with their strong defensive performance against Jacksonville.

The top of the list still features two dominant defensive teams.  San Francisco held the Los Angeles Rams to just 7 points, and Jared Goff was held to the lowest yardage total of his career.  The only other time Goff failed to reach 100 passing yards was in 2016, also against the 49ers.  

The Patriots gave up their first passing touchdown of the year to none other than Daniel Jones, but locked it up after that, picking him off three times.  New England's offense is still very average (16th in total offensive EPA), but the defense is just so good that they continue to hold a commanding lead on the No. 1 spot in our rankings.

As we look at these defense-led teams on top, let's break it down a bit more and see how each team stacks up defending the run and the pass.

The Patriots check in as the best passing defense by a pretty wide margin, and the fourth best rushing defense.  The 49ers are also in the top-7 in both pass and run defense.  A great defense might be hard to predict, but building a good one isn't a bad avenue to creating a winning team.

The Patriots, while undeniably dominating their opponents on defense, also have yet to face an offense with much success.  If we take away games played against the Patriots, their six opponents still stick out as below-average offenses, especially through the air.

One can't write off New England as just a product of playing bad offenses, though.  They are burying teams they're supposed to bury.  But one also can't completely write off the fact that they're only playing bad offenses.  How does this defense stack up against a highly efficient offense?  We may not know until Week 12 or 13, when they play Houston & Kansas City back-to-back.

The biggest factor in defensive EPA is turnovers.  Every coach preaches the importance of turnovers, and for good reason.  They've got the largest net change in EPA in most games, and they explain more than half of a team's EPA/play allowed.

Winning the turnover battle really is as crucial as coaches like to say it is.  The issue is that they are mostly random.  The number of turnovers a team forces early in the season tells us almost nothing about how many turnovers they will force the rest of the way.  Just last season, the Jets had 15 turnovers after 6 weeks, only to finish the year with 20 total.

The point of all this is that the Patriots aren't likely to see another 15 turnovers in the second half of the season, especially as their schedule gets (slightly) tougher.  And this goes the other way too.  The Colts and the Jaguars have more talent on defense than their EPA/play indicates, and they're also near the bottom of the league in turnovers.  Bet on them to turn that around at least a bit moving forward, especially if the Jaguars manage to convince Jalen Ramsey to come back and play for them.

At the end of the day, defense matters.  But it's not just built on talent, or scheme.  It's built on the opposing offenses and turnovers, which can fluctuate significantly throughout a season.  So don't get too down if your team's defense isn't perfect after six weeks, and temper your expectations if your team's defense is built on turnovers so far.