For decades the Lions offensive line has been a punching bag, both in physical and philosophical terms. This season is no different: fans have howled about the five-sack disaster in Minnesota, the abundance of penalties, and the continued inability to run impressively between the tackles. Nearly every Lions offensive lineman (excepting Rob Sims) has heard calls for his head on a pike, and it’s just barely October.

Line play was always one of the intricacies of the game; secret mojo that casual fans don’t perceive. Certain players or units are so consistently outstanding that analysts take pains to point them out, though, so most fans are dimly aware of “good” and “bad,” especially in terms of the quarterback’s time to throw.

Still, even hardcore fans can’t evaluate the offensive line in one full-speed viewing—at least, not without ignoring stuff like the ball and the outcome of the play. For the most part, fans judge their team’s offensive lines by the totality of their effort: number of sacks, number of penalties, average time to throw, perceived running lanes.

In recent years, though, the explosion of football information—and tools like DVR and NFL Game Rewind—lets us go back and see who really allowed Jared Allen’s sacks. Sort of.

If modern technology and analysis provide fans with a treasure trove of ways to evaluate their teams’ offensive line, what fans lack is any way to objectively compare that performance against others. When Cris Carter insisted Calvin Johnson is not an “elite” wide receiver, I slathered Carter’s good name in statistical napalm and lit a match.

When Lions fans say the offensive line “sucks,” I have few weapons with which to defend their honor—despite being sure the Lions’ line is a solid pass-blocking unit, and not a terrible run-blocking unit either. ESPN’s Ross Tucker explains:

It's not their fault. Or at least not entirely. That is the only logical explanation that can be drawn about the quality of offensive line play at the quarter pole of the NFL season. Before you assume that this is a column written by a former offensive lineman attempting to absolve his trench brethren of their inadequacies, consider the facts. If close to 75 percent of the fans in the NFL think their teams' offensive line stinks, maybe the problem isn't actually the offensive line but rather what they are being asked to do? At a minimum, fans and media alike need to look at the number of teams unhappy with offensive line play and realize that maybe this is the new normal. If that is the standard of performance for more than half of the teams in the league, then that is, by definition, the average.

Of course, the Internet’s gold standard in hardcore game footage review and line play evaluation is Pro Football Focus. I looked at the PFF team pass blocking grades over this year, last year, and the year before.

CHART?

Chart.

This is the distribution of PFF team pass block grades for 2009, 2010, and 2011 to date. The X axis is standard deviation from the mean, and the Y axis is the number of teams who fall into the half-standard-deviation tiers. “-3.0” is three standard deviations below the mean, “0” is the mean, and “+3.0” is three standard deviations above the mean.

The first thing that jumps out at you is the way the 2009 line appears to disappear. In fact, 2009 and 2010 had the exact same distribution above the mean: eight teams between the mean and one-half standard deviation above, six teams between +0.5 and +1, five teams between +1 and +1.5, and no teams two standard deviations or more above the mean. In both seasons, then 19 teams were graded above the mean.

In both seasons there was a hearty group of “above average” pass blocking lines; the majority of NFL offensive lines were a little bit better than the mean. On the downside of those two slopes, the distributions are similar. They seesaw with a gap of two or three teams from -0.5 down to -2.5, where they each have one. Both years share an overall shape: a few awful teams, several bad teams, some “meh” teams, then most of the NFL is between “okay” to “good,” with just a few “pretty good” pass-blocking lines and no “very good” or “great” ones.

A quarter of the way through this year, a different shape is emerging. Only 16 teams are grading out above the median, meaning four fewer “good” or “pretty good” pass-blocking lines. The Tennessee Titans are that outlying bump at +2.5; an entire standard deviation above the second-best Buffalo Bills.

After that, though, it’s more bad news: nine teams are at least 1.5 standard deviations below the mean, compared to four in 2010 and six in 2009. That’s 28% of the league’s offensive lines at “bad” or worse!

Now here’s the interesting bit. We see that so far in 2010, there are fewer relatively “good” pass-blocking lines and more relatively “bad” ones. But that’s only relative to each other in the same season. What about year-over-year?

PFF normalizes all of their grades, meaning these grades aren’t just the raw scores. The first season they graded (2008), they adjusted the grades so they averaged out to zero. In subsequent seasons, they’ve normalized their grades with the same factors as from 2008—meaning, grades from 2009 and 2010 and 2011 will compare directly to 2008 (and each other).

Look at 2009’s mean: -0.22, or almost exactly zero. This means that PFF’s raw pass-blocking grades (and in theory, leaguewide pass-blocking performance) was almost identical from 2008 to 2009. But in 2010 that mean dropped to -18.56. In 2009, a team that graded out at -18.56 would have been binned in the “-0.5 to -1.0” tier! If we do an incredibly crude projection of this season’s grades (multiply by four), the average 2011 team will grade out at -24.99, very nearly a full standard deviation below 2009’s mean!

This implies that leaguewide pass blocking performance has declined dramatically from recent norms. Not only has the distribution changed so that more teams are “bad” at pass blocking while fewer are “good,” the standards for “bad” and “good” are noticeably lower. [Ed. - Upon further review, I added a second chart. Was in danger of violating 1 picture/thousand words rule.]

Here’s a better way of seeing the year-over-year change: the 2009 grades are an almost perfect expected distribution between extremes, norms, positives, and negatives. The 2010 grades have a nearly-identical shape, just with an across-the-board decrease. The 2011 grades, though crudely projected, again reflect a change in distribution: there are far more bad-to-awful lines, and far fewer decent-to-good ones.

PFF detractors will be quick to claim this as proof of flaws in their methodology; that’s certainly possible. But it dovetails perfectly with what Ross Tucker has observed: teams are passing at a ridiculous rate, and increasingly using tight ends and running backs as targets, rather than blockers. They’re hanging their offensive linemen out to dry to spread the defense and the ball around the field—and it’s showing in both passing effectiveness, and pass protection grades.

Throughout all three seasons, the Lions haven’t been more than a half a standard deviation off the mean. They were just below league average in 2009, just above it in 2010, and are just below it as we speak. This is the most pessimistic assessment of the Lions pass blocking I could find.

Football Outsiders ranks the Lions' pass protection as third-best in the NFL, with an Adjusted Sack Rate of 2.9%. The New York Life Protection Index currently ranks the Lions’ O-line 7th-best at keeping the quarterback clean. In both cases, they’d likely be topping the charts if it weren’t for the Minnesota game . . . which, given my suspicions about the Vikings’ eternally-rowdy home atmosphere, that really grinds my gears.

Jeff Backus is not Walter Jones. We know this. To our untrained eyes, the pass protection seems “lousy,” and the data suggests that our untrained eyes are absolutely right. But if our “lousy” is just about as good as everyone else’s “lousy,” then it’s not really all that lousy. And, if our “lousy” is really much better than everyone else’s “lousy,” as FO and the NYLPI imply, then we’d better learn to appreciate what we’ve got.