(For this post, note that statistics are from pro-football-reference.com. I will be talking about adjusted passing YPA. The adjusted just means that it takes sacks into account. For example, let's say that Peyton Manning goes 14-24 for 156 this week and gets sacked once for 6 yards. Then his YPA would be 150/25 = 6. 150 is net yards passing (156-6) and 25 attempts includes the time when he dropped back to pass but was sacked.)

When Mike Tomlin was hired as the the new Steelers head coach, like many fans I looked to see what his background was. While he was a db coach with TB, the secondary played pretty well and they definitely shined in the 02 Super Bowl. But you never know what the exact impact of an assistant coach is, so it's hard to know how much of that success was due to Tomlin. And as well as the TB pass defense played in the Super Bowl, it's still just one game and some thought that they had an advantage since Gruden was well aware of Oakland's and Gannon's tendencies.

Once Tomlin moved on to Minnesota, it wasn't Minny's pass defense that improved, but rather their run defense. In 2005 (the year before Tomlin), Minny allowed 5.9 passing YPA and 4.0 rushing YPA. In 2006 (with Tomlin as defensive coordinator), Minny's allowed 6.1 passing YPA but only a miniscule 2.8 rushing YPA. But that's only one year, so who knows what would have happened if Tomlin had stayed.

Last year, Tomlin's first year as head coach with the Steelers, I noticed that the Steelers allowed very few yards per passing attempt.  In fact, they allowed only 4.9 YPA through the air while allowing 4.0 on the ground. (Unfortunately, I don't have the rushing YPA before Aaron Smith got hurt.)

To put that 4.9 into perspective, consider that it matched the best defensive passing YPA the Steelers ever managed under Cowher, whose teams posted a 4.9 in 1994 and (somewhat surprisingly to me) in 1996.

This year, however, the Steelers have taken it to another level. They are allowing a paltry 4.2 passing YPA. That is easily the best mark since the glory days of the 70s. Meanwhile, the team is allowing only 2.9 on the ground.  (That 2.9 would actually be better than any Steeler defense under Cowher or Noll.) Those numbers are incredible halfway through this season. It's even more impressive when you consider that the team has had to overcome multiple injuries on the defensive side of the ball, although none have been season ending (knock on wood) thus far and the 3 most important players on defense (Harrison, Woodley and Polamalu) have remained relatively healthy. It's also worth noting that the offense hasn't exactly helped the defense that much either, often putting the Steelers defense in many short field situations.

If the Steelers defense can maintain this pace, we may be seeing the best Steeler defense since the 1970s.*

As an aside, to appreciate how good those 70s Steeler defenses consistently were, consider that from 1972 through 1979 (8 years), the Steelers allowed a defensive YPA of 4.9 or less 7 times. In 1974, they posted a measly  3.7.

* I obviously put a great deal of stock into defensive YPA, especially passing YPA. But there are other stats that I value as well, mostly turnovers and points allowed. I readily admit that I can't really say that this Steeler defense would be the best since the 70s withouth looking at these categories. For example, this defense is on pace to allow 232 points, which compares favorably to the 234 that the 94 defense allowed. However, this year's team is only on pace to force 24 turnovers, while the 94 edition forced 31.