The old adage isn't always true, but for the New England Patriots, defense certainly has won championships.  After years of patchwork secondaries and anemic pass rushes, everything came together for the Pats defense in 2014.  And while the unit didn't produce the same league-leading numbers as the defenses from the early 2000s, premier talent like Darrelle Revis, Devin McCourty and Jamie Collins gave the Patriots the ability to combat virtually any offensive style.

Unfortunately, the reality of the salary cap made that defense a one-year wonder.  Revis was never a realistic option to stay after the New York Jets sold the farm for their old friend, and though the Pats could have stomached the contracts of Vince Wilfork, Kyle Arrington and Brandon Browner, their long-term cap health is probably better off without those vets, whose combined cap figure would have been just over $19 million for 2015.

However, the 2015 doesn't necessarily need to be worse than its predecessor, contrary to popular belief.  Football Outsiders ranked the Patriots defense 12th overall by DVOA, while Advanced Football Analytics placed them eighth by Expected Points Added.  Those are certainly nice spots, but New England is not trying to live up to the 1985 Chicago Bears.

The most important realization Patriots fans should have is that the defense will be very different in 2015, both in terms of personnel and schematic strengths.  Laying out one early depth-chart projection below, let's highlight where this defense can win in 2015 and where it will likely struggle to tread water.

The Good

A Better Pass Rush

This is kind of a captain-obvious point, so let's try to flesh out what "better" means.  By total production, New England's pass rush was below average in 2014, as the Patriots finished 23rd in sack percentage, per TeamRankings.com, and 20th in Football Outsiders' adjusted-sack-rate metric (which adjusts for opponent and down-and-distance).

In hindsight, it's a little surprising the Pats won the Lombardi Trophy behind those mediocre rate numbers.  New England was the first Super Bowl champion to finish outside the top 10 in adjusted sack rate since the 2009 New Orleans Saints, and over the past 10 years, those two plus the 2006 Indianapolis Colts were the only champions to rate in the league's lower half on both sack metrics:

Now, edge defender is the deepest position on the 2015 roster, with the possible exception of offensive tackle.  While Bill Belichick has done well to unearth rare three-down linemen during his time in Foxborough, actually playing Chandler Jones and Rob Ninkovich every down has minimized each player's efficacy on the money passing downs.  As Pro Football Focus' Pass Rushing Productivity metric illustrates, New England's only reliable source of pressure last year came on second-level blitzes from Jamie Collins and Dont'a Hightower:

While Collins and Hightower were extremely effective in that role, every great pass rush possesses a multitude of options that can flummox offenses.  That's where the real value of the Patriots' newfound depth comes in, for in past seasons, the defensive line has been among the most static and boring units on the team in terms of schematic usage.

Being predictable and mediocre has its consequences.  It's probably not a coincidence that the Patriots' pass defense finished 30th in DVOA against tight ends and 14th against running backs, per FO, as teams rarely needed to utilize extra blockers against New England's straight four-man rush.  Consequently, opposing offenses had extra chess pieces to create advantages in the passing game.

Here's an example of this concept in action during the Pats' Week 13 contest against the Green Bay Packers.  New England was in its staple Cover 3 coverage, but even though the Patriots were dropping seven into coverage, Green Bay's formational alignment put the defense at a natural numbers disadvantage on the strong side.  Consequently, Brandon Browner was left in no-man's land, leading to an Eddie Lacy 12-yard reception and a first down:

A better pass rush isn't going to magically eliminate all disadvantages—after all, good offenses scheme to create those edges for themselves.  But with better and fresher pass-rushing personnel, perhaps the 2015 Pats can punish teams like the Packers for not keeping Lacy or Andrew Quarless in the box as an extra blocker.

We've heard about the much-ballyhooed "NASCAR" package tossed around this spring, though that tease has been around for a few years now.  However, it's never been closer to becoming a reality, as 2015 will be the first time in recent memory that Belichick can utilize four true defensive end types on passing downs.  A quartet of Jabaal Sheard and Rob Ninkovich on the edge with Chandler Jones and Dominique Easley inside is the type of formation that would command offenses to game plan more conservatively.

Ultimately, this is what "better" really means, as a more unpredictable pass rush would have a trickle-down effect to the depleted cornerback corps.  However, it's not entirely on the front seven to carry the pass defense, as the other half of the defensive backs crew has been strangely overlooked this offseason.

Versatility at Safety

NFL custom has indoctrinated us with the belief that cornerbacks are significantly more valuable than safeties.  The money does the talking here; according to Spotrac, the AAV (average annual value) of the 10 highest-paid cornerbacks averages out to $11.6 million, while that figure drops to $8.1 million for the 10 richest safeties.   

But it seems as though that mantra is dependent on scheme.  Yes, Richard Sherman is a perfect fit for Seattle's press-man hybrid coverage, but the Seahawks wouldn't be a generational defense without Earl Thomas serving as this generation's best center fielder.  New England lost its version of Sherman this offseason, but can Devin McCourty keep the secondary afloat?

To test this, I took a look at Pro-Football-Reference's Approximate Value metric.  Since moving to safety, McCourty has posted an average of roughly 8 AV per season (rounding up).  Last year, the 32nd-best cornerback by AV, Desmond Trufant, posted an AV of 6.  Looking at some recent examples, here's a sampling of defenses that had a safety post an 8 AV season or better, while also failing to produce at least one cornerback with a 6 AV season or better:

OK, so maybe the league execs do know what they're doing (surprise, surprise).  Poor Eric Weddle and Jairus Byrd are superb talents that have been left out to dry multiple times by poor surrounding talent.  On this alone, Patriots fans might find reason to feel nervous.

However, McCourty is also not a one-man show at safety, as the Patriots possess a pair of box safeties in Patrick Chung and second-rounder Jordan Richards, as well as third-year pro Duron Harmon, who has played various positions during his tenure in Foxborough.  None of these McCourty partners are game-changers, but they offer a wide spectrum of skill sets that could allow Belichick to scheme his way around some talent deficiencies.

The "big nickel" package is a particularly intriguing personnel grouping that could allow the Patriots to get their best defensive backs on the field, depending on how the cornerback race shapes up.  Instead of placing a slot cornerback on the field, the big nickel personnel calls for three safeties, with one often dropping down to cover a tight end.

The Pats rolled out a modified version of this on their game-sealing pick against the Baltimore Ravens in the Divisional Round.  New England actually has four safeties (partially because Browner got hurt in this game).  McCourty dropped down to cover Kamar Aiken in the slot, while Tavon Wilson and Chung combined to double-team Joe Flacco's first read, Owen Daniels.  That left Harmon as the roaming center fielder, and the young safety made the correct read to the sideline for the interception:

Here's the more conventional three-safety example against Miami.  Harmon was once again the deep center fielder, as McCourty rolled down into the box at the snap.  He and Browner appeared to have a "thumbs" coverage call, with McCourty taking the under and Browner the over zones.  However, it's Chung's range that makes this play, as he rolled out with Ryan Tannehill and gained enough depth to deflect this pass for an incompletion:

These personnel packages enable the Pats to better disguise their coverages, while also providing more range in underneath zones than a linebacker might supply.  If New England turns to more zone concepts, as many would expect, tapping into the safety group's instincts might be a better bet than relying on a callow corner.

McCourty seems unlikely to stick to the deep center-field role he's inhabited the past two-and-a-half seasons, as the Patriots will need his versatility on the back end more than ever.  By using safeties who understand the scheme and can cover a multitude of roles, the Patriots can fully tap into their best player's own strengths and lift their coverage as a whole.

The Bad

What's Their Cornerback Identity?

The issue is not so much the Patriots' lack of talent at cornerback, but rather the ill-fitting smorgasbord of strengths and weaknesses that comprise the unit.  Belichick garners praise for his ability to place his players in positions that highlight their strengths, but how can he do that if a unit's strengths are wholly unclear?

This is a bit of an oversimplification, but one can roughly divide the Patriots cornerback corps into two camps: smaller, more agile players who would fare best using their ranginess in off coverage, and thicker, more physical corners who would play better with press principles.  Logan Ryan and Robert McClain fall into the former category, while Malcolm Butler, Bradley Fletcher and rookie Darryl Roberts fit the latter.

That grouping doesn't include players like Dax Swanson, Justin Green or any of the Pats' three undrafted rookies.  Football Outsiders' Andrew Healy highlighted UAB's 6'3" Jimmy Jean as a potential UDFA who could crack the roster, and more so than any other position, cornerback looks ripe for a sleeper to emerge during training camp.

The current personnel grouping reminds me a bit of the first half of the 2012 season, before Aqib Talib arrived via trade.  That Patriots defense started McCourty and Alfonzo Dennard as its top perimeter corners, two very different players who didn't necessarily belong in the same scheme.  New England utilized lots of "Quarters" two-high coverages during that time, but Belichick also sometimes allowed Dennard to press while McCourty played bail:

Both received safety help in the above screenshots and had relatively easy assignments, only needing to cover the deepest outside-breaking route.  But McCourty and Dennard were both allowed to release into those reads in ways that best suit their skill sets, an example of a small tweak the Patriots can make to tailor their coverage to their misfit cornerback groupings.

The release of Kyle Arrington also suggests that the Patriots would rather play more press coverage, something that would place the secondary at risk but better accentuate the real strength of the defense, the pass rush.  Note that press coverage does not necessarily equate to man coverage; that was a luxury the Pats enjoyed last season, but no one currently on the roster appears to possess the size and match-and-mirror discipline to effectively pull that off for extended snaps.

Regardless, a Butler-Fletcher duo on the perimeter could represent a move to more Cover 4 press principles (a coverage Bleacher Report's Matt Bowen broke down last year).  That's obviously speculation at this point, and it does not account for the distinct possibility that a Jean or Swanson type makes waves.  This year's cornerback crew feels like last year's offensive line, the unit that experiments with personnel into the season and struggles until it settles on a workable starting group.

Volatility at Defensive Tackle

It's hard to find much fault with the front seven, but defensive tackle looks like the position with the widest gap between its floor and ceiling.  First-rounders Dominique Easley and Malcom Brown could potentially form a decade-long duo in the middle of New England's defense, but if we're talking solely about 2015, neither is a bet to even become an average player.

Belichick has had success with young interior duos before, as rookie Vince Wilfork and fourth-year pro Richard Seymour were huge assets on the 2004 championship-winning squad.  Seymour was already a two-time All-Pro selection at that point, though, a far glitzier resume than either Easley or Brown can boast at the moment.  It's not a stretch to suggest that New England has the least proven DT duo in the league—using the projected depth charts from Ourlads, here's a look at the combined career AV of the starting defensive tackles on 4-3 teams:    

I'm skewing the data a bit by picking Brown and Easley, as Ourlads actually projects Alan Branch and Sealver Siliga as the Pats' starting defensive tackles.  The Branch-Siliga duo bumps up New England's combined AV to 36 due to Branch's time as a starter in Seattle, which would place them ahead of five of the above teams.  Still, that projection doesn't really reflect that Easley and Brown are likely to receive the majority of the snaps, while Branch and Siliga might be deemed "starters" due to their value in the base packages that typically open games.

I've already broken down Easley (here) and Brown (here) in depth, so head over there if you need a refresher on either player.  Easley's success is probably more vital to the Patriots' immediate future, for there isn't a player on New England's roster whose skill set overlaps significantly with that of the 2014 first-rounder.  Brown might develop into a versatile three-down player who moves around the line, but for next year, anything more than plus run defense should be considered a bonus.

Recent precedent does suggest a promising future for the Brown-Easley duo.  The most similar situations that come to mind are the 2011 Detroit Lions and 2013 New York Jets, both of whom boasted a first-round defensive tackle tandem on rookie contracts.  Nick Fairley remains enigmatic, but the trio of Ndamukong Suh, Muhammad Wilkerson and Sheldon Richardson have all blossomed into excellent players and foundational pieces for their respective defenses.

Not all interior duos turn out so swimmingly—just ask the Kansas City Chiefs, who spent top-five picks on Glenn Dorsey and Tyson Jackson in 2008 and 2009—but the odds are in New England's favor in this instance.  For once, the Patriots' Gang Green rivals represent a template that the Pats would be happy to follow.

Predictions

Having gone in-depth on a few positional strengths and weaknesses, here are a few quick-hit predictions to chew on before offseason camp work kicks into gear.

1. Run Defense Will Improve

The Patriots run defense improved from the disastrous 2013 campaign, but New England was still a relatively middling unit, finishing 13th in DVOA and 11th in yards per carry allowed.  The Pats were notoriously poor in short-yardage situations, which was pointed out ad nauseam after the Seahawks' infamous Super Bowl goal-line play call.

Provided reasonable health, anything less than top 10 in both stats this season will be disappointing.  The Patriots' front seven is as deep as it's been in recent memory, not only with sub-package specialists, but with run-stuffers like Siliga, Branch and the readopted Brandon Spikes.  Given New England's secondary holes, opposing offenses should exhibit a fairly large skew in their run-pass play-calling distribution.

2. Turnovers Will Go Down

Advanced Football Analytics' Brian Burke has illustrated that turnovers are over 50 percent luck-based, as year-to-year correlations are extremely fickle.  New England had the 10th-most takeaways and second-best turnover margin in the league last season, but that seems quite likely to regress in 2015. 

Remember, part of the reason the Pats have always forced so many turnovers is because they're typically better than their opponent and consequently leading.  Opponents desperate for quick scores tend to make riskier play calls, which leads to a higher turnover rate.  With Jimmy Garoppolo starting a quarter of the season, though, the Pats are unlikely to have that kind of edge, which could drive down their overall takeaway numbers for the entire season.

3. Defense Finishes 15th-20th in Overall DVOA

I'm predicting a slight regression from last year's defense, but not the disaster that the 2011 unit represented.  Barring a slew of injuries, New England should hold the edge in the trenches over most of their opponents, something that should help stave off much of the secondary's staggering regression in talent.

A shutdown defense undeniably makes things easier, but the 2012 Ravens (19th in defensive DVOA), 2011 Giants (19th) and 2009 Saints (17th) are all examples of champions who survived without top-half defenses.  The 2015 Patriots defense will be quite different and perhaps slightly worse than its predecessor, but that alone should not eliminate New England from serious Super Bowl contention.