The New England Patriots are always looking to make roster improvements. Despite winning the Super Bowl, Bill Belichick believes there is always work to do. After having just beaten the Atlanta Falcons to win Super Bowl LI, Belichick’s take away was that as a result of the title run, New England was already five weeks behind the 30 other teams in preparing for the 2017 season.

Some low hanging fruit for the Patriots entering the offseason was the defensive interior. Last year, New England ranked 19th in run defense DVOA and 26th in defensive adjusted line yards. This was an area with an easy path to improvement.

The Patriots already employed one defensive monster in Lawrence Guy. The trick was either upgrading the teammate directly next to him or bolstering the depth. New England chose to upgrade the teammate next to Guy. The only real move the team made in this department was bringing in Mike Pennel to replace the departed Malcom Brown.

Belichick doesn’t need his defense to be an elite run stopping unit. The entire Patriot blueprint is to be the team with the fewest amount of weaknesses, not the greatest amount of strengths. If New England can simply go from below average run defense to above average run defense, it will be mission accomplished.

Lawrence Guy

The overlooked Guy finished 2018 as ProFootballFocus’ 10th ranked interior defensive lineman. More so, he finished with the sixth highest run defense grade among the position. The statistical achievements continued as Guy tied for the third most run stops among interior defenders in 2018, and had the fourth highest run stop percentage at the position among those that played at least 169 run snaps.

Case in point, Guy was an elite run defender last season. However, Guy could improve and help New England’s larger cause by becoming more viable as a pass rusher. Guy was OK creating interior pressure in 2018, as he ranked 32nd in PFF’s pass rush grades among interior defenders that logged at least 465 total snaps.

Reason for optimism in this department is Guy’s performance in Super Bowl LIII. Against the Los Angeles Rams, Guy tallied three quarterback hurries and one quarterback hit. For context, Guy accumulated 11 hurries during the entire 2018 regular season. Guy was a disruptive force during the Super Bowl.

Guy goes back to the well for another pressure, jolting Sullivan before dipping the shoulder and ripping through the block to speed up Goff's clock. ST ace Albert McClellan, who also prevented a punt block TD, makes the open field tackle on the check-down to Gurley. pic.twitter.com/y9UZmaoRUa — Taylor Kyles (@tkyles39) February 9, 2019

Expecting Guy to rack up three pressures per game next season is unrealistic. He has never been that dynamic an interior rusher, and only four interior defensive linemen cracked 40 quarterback hurries in 2018; Aaron Donald (65), Fletcher Cox (60), Geno Atkins (46), and Chris Jones (44). That is quite literally the best of the best.

However, Guy doesn’t need to be on their level. Circling back, Belichick just wants to have the fewest weaknesses, not the most strengths. If Guy can experience a breakout season where he compiles 20-25 quarterback hurries in 2019, that’s the improvement for which New England is seeking.

Mike Pennel

New England brought in Pennel to upgrade from Brown. Looking through a narrow view of 2018 performances leads us to believe an upgrade was accomplished. Pennel ranked 14th among interior defenders last season, according to PFF, while Brown ranked 85th. Pennel’s 87.1 grade blows Brown’s 64.4 out of the water.

There are two reasons for caution, however, before fully deeming the player swap an upgrade; a micro and macro sample size. Last year, Pennel played 357 total snaps to Brown’s 507. While neither defensive lineman was an every-down player, Brown played 142% of Pennel’s snap count. Furthermore, in five seasons, Pennel has only one other season graded above a 60 (73), while 2018 was the first time in Brown’s four year career where he graded below a 70.

Getting more specific about the discrepancy in play last season, Pennel significantly outperformed Brown as both a run defender and a pass rusher. Pennel outpaced Brown in the run defense grade category 87.0 to 64.0. In fact, Pennel had the 11th highest run defense grade among the position. Additionally, Pennel looks to be an upgrade as an interior disruptor as well, as his outpaced Brown 74.5 to 60.6 in PFF’s pass rush grading. Pennel had the 13th highest pass rush grade among interior defenders, again ranking in the top 15 at his position.

As evidenced by the comparison, Pennel performed well as an interior defensive lineman in 2018. He ranked 14th in run stop percentage among those that played at 167 run defense snaps and tied for the 32nd most run stops with the same minimum snap requirement.

Similar to Guy, where Pennel can really provide a boost for the Patriots is if he can contribute as an interior pass rusher. Pennel flashed the ability to be a disruptive force in 2018.

Bull rushing on the right guard. Pushes him back into Mariota then gets his hands up to deflect the pass. #Patriots pic.twitter.com/4jksiAEpuA — Evan Lazar (@ezlazar) March 14, 2019

One more: good first step quickness. Beats Andrews clean with the arm over to get to Brady. #Patriots pic.twitter.com/9O5CbuACQ5 — Evan Lazar (@ezlazar) March 14, 2019

In case you needed a reminder, David Andrews is a very good guard.

Danny Shelton

Danny Shelton decided to stick around New England as opposed to leaving in free agency this offseason. At the time of the trade last year, this marriage appeared destined to be a one-year rental. However, Shelton signed on for one more year in Foxborough for an attempted repeat, before he goes back out onto the market in 2020.

Shelton is a solid defensive tackle capable of being a starter. He posted a 78.8 overall grade last season, with a 79.8 run defense grade. He has been consistent over the past three seasons, grading out at 82.1, 70.3, and the aforementioned 78.8.

Shelton contributes mostly in the run game. His 79.8 run grade last year was 27th among the position. In 2017, Shelton’s 79.5 run defense grade ranked 25th at the position among those that played at least 450 snaps. In 2016 he was one of the best run defenders in the NFL, as his 83.7 run defense grade ranked 6th at the position, again among those that played at least 450 snaps.

Adam Butler

Adam Butler is a former undrafted free agent who has a special place in Belichick’s heart. In two seasons on the roster, Butler has posted PFF grades of 56.8, and 58.3, while totaling 36 tackles. Yet, Belichick does not move on or look to upgrade the death behind his starters, despite the practically zero cap ramifications of releasing Butler.

The lack of impact is not due to lack of opportunity, either. Butler logged 480 snaps in 2018 and 474 in 2017. Last year, Shelton saw the field for 344 snaps and was the clearly superior player to Butler. Perhaps Belichick just has an affinity for undrafted or late round players that work hard enough to stick on the roster. Whatever the reason may be, Butler is the weak link of this four-man core.

The Aggregate

As mentioned at the outset, New England is returning their main group with the exception of a single player swap. That swap, Brown for Pennel, has the potential to pay large dividends.

Skepticism is warranted, however. Is Guy really the person we saw in 2018? That was by far his best season as a professional. Some regression to the mean in his performance shouldn’t come as a surprise to anyone should it happen.

All in all, this is at worst a mediocre group, with the ability to be above average. If the Patriots can move from below average to above average in this area, they’ll have done their job.

Jonathan Rosenberg is a writer for PFN covering the New England Patriots. You can find him @frosted_takes on Twitter.