We know that the Seahawks pass defense is historically good, but the title of this post sounds like it was written by a Seahawks homer, right? I mean, who else besides a green-and-blue fanboy (or maybe Richard Sherman or Earl Thomas) would write something as absurd as “Seattle’s pass defense is so good that teams are afraid to throw on them!!!”

The thing is, it’s kind of true. Seattle faced only 568 pass attempts (including sacks) during the regular season, the sixth fewest in the NFL.  Some of that is due to the Seahawks pace on offense and dominance of a defense that prevented sustained drives; even still, opponents passed on “only” 57.4% of all plays against Seattle.

Seattle ranked below average — 18th — in percentage of pass plays faced, but there’s a reason I put only in quotes. Seattle held an average lead over every second of game play this year of 5.6 points, the third best mark in the NFL. Denver and San Francisco were the only teams to play with larger leads, and they ranked 6th and 7th in percentage of plays faced that were passes. This is hardly a newsflash — teams generally throw often when trailing — but that wasn’t the case with 2013 Seahawks.

When Steve Buzzard used the Game Scripts data to determine defensive pass identities, he found that teams were more hesitant to pass against Seattle (once adjusting for the score and strength of schedule) than against any team in the league. I thought it would be interesting to take another crack at measuring this effect. We can use the score differential after each of the four quarters of the game to determine how many pass attempts (as a percentage of total plays) a team *should* face.

I ran a regression of every team game from 1970 to 2013 using the following inputs:

• The score differential after the first quarter;
• The score differential after the second quarter;
• The score differential after the third quarter;
• The score differential after the fourth quarter;
• The league average pass/ratio during that season

The best-fit formula to predict pass ratio is:

Pass Ratio = .29% + .046% * 1QM + .076% * 2QM + .195 % * 3QM + .245% * 4QM + 99.5% * LgAvgPassRatio

How does that formula work? Let’s use the Seahawks game against Arizona as an example. In that game, the score was tied after each of the first two quarters, Seattle trailed by 3 after the third quarter, and Arizona won by seven. The league average pass ratio in 2013 was 58.4%, so we would expect Arizona to pass on 56.1% of all plays in a tight game won by the Cardinals. Instead, Arizona passed on just 38.6% of all pass plays. That’s a difference of over seventeen percent. In eleven of Seattle’s 16 games, the opponent passed less frequently than we would expect. And over the course of the season, Seahawks opponents passed nearly six percent less often than we would expect, given the scores in the games. That was the largest differential of 2013. The table below shows the Expected P/R ratio faced (based on the scores after each quarter), the actual P/R ratio seen, and the difference:

What about historically? I ran the same process for every team season since 1970. Seattle ranks “only” 31st as far as seeing less passes than you would expect, although part of the reason for that is the team’s strong run defense. For example, the number one team, by far, in this metric, was the 2006 Colts. But that year, Indianapolis ranked last in yards per carry allowed. In other words, nobody was passing against Indianapolis that season, but the reason behind it wasn’t a dominant pass defense but a terrible run defense (and maybe a desire to keep Peyton Manning off the field).

Among teams that ranked in the top 10 in yards per carry allowed, Seattle would rank 4th in pass/run ratio differential — behind only the 2007 Colts, 1973 Dolphins, and 1990 Bills.

We can also look at the other side of this coin: which teams faced significantly more passes than you would expect? Below are the top 50 teams since 1970. The top team is not much of a surprise: the 2006 Vikings. That year, Minnesota posted the 3rd best YPC allowed average since the merger, and nobody wanted to run against those Vikings. The 1998 Chargers (who allowed the 2nd fewest yards per carry since the merger) also make the list, but the 2000 Ravens do not: