No one suggests that the Patriots defense is good, or even average. For starters, well, look at the starters. Here was New England’s starting lineup this weekend against the Broncos:

Casual fans have heard of Wilfork and Mayo, and McCourty was one of the top rookies in the league last season. But don’t feel bad if you’ve never heard of Deaderick (2010 7th rounder) or Love (undrafted) or Fletcher (undrafted from Montana State) or Slater (5th round draft pick — at wide receiver — who converted to safety in the middle of this season), and it’s not like Ihedigbo (undrafted, special teams ace for the Jets) , Arrington (undrafted, Hofstra) and Ninkovich (5th round pick by New Orleans) are high profile players, either. Now that Andre Carter — New England’s best pass rusher — is out for the season, the situation looks even worse. And among the “name players” on the Patriots’ defense, only Mayo (who missed several games earlier this season) isn’t having a disappointing season.

The Patriots do not have much talent on defense. So it’s not too surprising that the Patriots rank last in the league in yards allowed. But the situation is even bleaker than that. The 1981 Baltimore Colts were one of the worst teams in football history; they’re also the only team that allowed 5800 or more yards in the first 14 games of the season. Well, they were: now the Patriots have joined the list.

But the Patriots total defense is still better than the Patriots pass defense. Until this season, no team had ever allowed more than 3,910 passing yards after 14 games; the Patriots have allowed 4,154.

Part of that historical ineptness is because the Patriots often play with the lead. New England has faced the third highest number of pass attempts this season, and ranks 30th (as opposed to 32nd) in net yards per pass attempt. So instead of having a historically terrible pass defense, it’s probably fairer to just note that they have one of the league’s worst pass defenses. New England’s rush defense isn’t very good — the Pats rank 26th in yards per carry allowed, and because they face so many more passes than rushes, 19th in rushing yards allowed.

But New England ranks 14th in points allowed. That means despite a terrible pass defense and a bad rush defense, the Patriots actually have allowed fewer points than the average team this season. So what gives?

A common explanation is that the Patriots play a ‘bend but don’t break’ style of defense. That sounds good, but New England is fielding the same collection of no-names regardless of where the opponent’s line of scrimmage is. The Patriots are 13th in red zone defense; that’s good, but nothing special.

New England has allowed only one non-offensive touchdown to their opponents, a pick-six by Drayton Florence in Buffalo’s victory over New England in week three. New England is one of 7 teams to allow just one return touchdown this season; the 49ers are the only team with zero. Since the average team has allowed 3.2 return touchdowns this season, you could say that the Patriots’ “points allowed” production overrates their defense by about 15.5 points, since most defenses get about 22.5 points added to their ‘points allowed’ column through no fault of their own.

Another reason why the Patriots appear to hold opponents off the scoreboard is because they simply don’t face that many possessions. Points per possession, or points per drive, is a more important statistic than raw points allowed. Allowing 24 points in a game where your opponent has 10 drives is more valuable than allowing 24 points when your opponent has 13 drives. That’s because if your opponent has 13 drives, you probably have around 13 drives, too. Each team has the same number of drives in every game, give or take some return touchdowns or fumbles, one team having the ball to end both halves, and a few other anomalous events like winning the overtime coin toss or recovering an onside kick.

Because New England goes on many long drives on offense and allows long drives on defense, New England’s defense has faced the 6th fewest drives against this year (and the 4th fewest drives on offense). The Patriots have allowed 38 yards per drive (most in the league by over two yards) and 1.91 points per drive, 23rd best. Points per drive allowed excludes non-offensive touchdowns, so a 23rd-place ranking in points per drive allowed is a better measures of New England’s defense than their 14th-place ranking in points allowed.

Because of a great offense and a good punting unit, the Patriots defense is rarely placed in a bad situation. New England rarely turns the ball over (third fewest in the league) and gains so many yards (2nd most) that they’re not giving the opponent the ball in a position to score. In fact, New England’s opponents have the 2nd worst average starting drive position of any team in the league (#1 is San Francisco, a team that seems to have been teleported straight from the ’70s) — the 24-yard-line.

So New England opponents have few possessions in most games, because there just aren’t many three-and-outs by either team. When you play New England, don’t expect to ever get the ball in good field position. The Patriots have been pretty good in the red zone — New England has intercepted 6 of 79 pass attempts against them when backed against their own end zone (7.6%) while the rest of the league has intercepted just 2.9% of such passes. One could argue that this is because New England’s red zone defense is just better than their regular defense, but the more likely explanation is some random luck. A few tipped passes — like this Santana Moss interception — can greatly influence your interception rate on a small number of attempts.

So how do you bridge the wide gap between a defense that ranks #32 in yards allowed and #14 in points allowed? First, you recognize that the offense puts the defense in a great position, by rarely turning the ball over, keeping the defense off the field and giving the opponent terrible field position. If you can be overrated at #32, the Patriots’ defense is, because while New England is #32 in yards allowed that’s despite not facing many drives. The Patriots are an even worse #32 in yards allowed per drive. And while the Patriots are “only” 23rd in points allowed per drive, a big reason for that is opponents have terrible field position against the Pats. Not only is the Patriots’ defense usually fresh, but they have a lot of green between their own end zone and the line of scrimmage. New England’s often playing with a lead, which forces their opponents into riskier tactics, which explains why the Pats are 5th in the league in turnovers forced despite not having much individual talent on defense. And, of course, every turnover forced is a drive that does not require any more defense, and the Patriots are 3rd in turnovers forced per drive. Next time you hear someone say that the Pats are a ‘bend but don’t break defense’ the appropriate response is ‘then why do they force so many turnovers?’

The Patriots red zone defense has been pretty good, but that’s based on a small sample size (and it’s been far from great). The Patriots aren’t a historically great red zone team, as New England ranked 22nd, 21st and 31st in red zone defense in 2010, 2009 and 2008. In 8 of 14 games this season, the Pats have led by a touchdown or more at halftime; in another 3, they led by a touchdown or more at the end of the third quarter. The Pats lost two of the other three games, and could have lost the third if the opposing coach hadn’t been so conservative. If the Patriots offense wasn’t so good, this would be an all-time bad defense in points against, too. Make no mistake about it, the Patriots are much closer to being the 32nd best defense in the league than the 14th.