Last Monday, I provided some initial thoughts on the relative values of completion and passing first down percentage. The next day, I looked at how teams with disparate performances in those two metrics. And last Wednesday, I looked at the best passing offenses in NFL history in first down rate on passing plays.

Today? A look at the best pass defenses at preventing first downs.  This time, I am also going to era adjust these ratings. In 1969, the Vikings faced 459 pass plays (410 pass attempts, 49 sacks) but allowed only 88 passing first downs. That’s a remarkable rate of just 19.2%, the best since World War II.   It’s also the best rate on an era-adjusted basis.  The league average in the NFL in 1969 was 29.0%, which means this iteration of the Purple People Eaters was 9.8% better than league average, the highest differential ever.

The table above shows the top 200 pass defenses at preventing first downs.

• Since 2010, the best pass defenses were, in order, the 2015 Broncos, 2012 Texans, and 2014 Bills.
• In the ’00s, the best pass defenses were the 2009 Jets, 2002 Bucs, 2004 Broncos, 2008 Eagles, 2000 Ravens, and 2008 Steelers.
• In the 1990s, the best pass defenses were the 1999 Bucs, 1991 Redskins, 1991 Eagles, 1991 Saints, and 1999 Ravens.
• The ’80s? The ’84 Bears, ’85 Bears, ’89 Vikings, ’80 Rams, ’89 Broncos, and ’84 Raiders.
• The ’70s? The ’71 Vikings, ’75 Steelers, ’74 Steelers, ’77 Falcons (of course), ’83 Dolphins, ’70 Vikings, ’75 Vikings, and ’79 Bucs.
• The ’60s? The ’69 Vikings, ’63 Packers, ’67 Raiders, ’62 Packers, ’67 Packers, ’67 Rams, and ’62 Bears and Lions.
• The ’50s? The ’54 Eagles, ’54 Browns, ’58 Bears, ’59 Bears, ’57 Browns, and ’52 49ers.

As always, please leave your thoughts in the comments.