Last Sunday a couple friends and I were watching the Ravens-Dolphins playoff game and we were talking about how good both Baltimore and Miami’s defenses were this season. Then we started to gab about other top defenses in the league and the thought dawned on me – all the good defensive teams play outdoors.

Think about it. What teams had the best defenses in 2008? Pittsburgh, Baltimore, Philadelphia, Washington and the Giants all ranked in the top five – all outdoors teams. Granted, Minnesota was No. 6, but the next dome team was Indianapolis at No. 11.

Out of the eight dome teams (I’ll count both Dallas and Arizona as dome teams), five of them (Arizona, Atlanta, New Orleans, St. Louis and Detroit) finished in the bottom half of the league in total defense. In 2007, six of the eight teams finished in the bottom half. In 2006, five teams finished in the bottom half. In 2005, four of the seven dome teams (Arizona was outdoors before 2006) finished in the bottom half and in 2004, six of the seven dome teams ranked in the bottom half defensively.

Here’s a breakdown of how each dome team has done defensively since 2002:

Arizona 2006-2008: 29th; 17th; 19th
Atlanta 2002-2008: 19th; 32nd; 14th; 22nd; 22nd; 29th; 24th
Dallas 2002-2008: 18th; 1st; 16th; 10th; 20th; 13th; 9th; 8th
Detroit 2002-2008: 31st; 24th; 22nd; 28th; 32nd; 32nd
Indianapolis 2002-2008: 8th; 11th; 29th; 11th; 21st; 11th;
Minnesota 2002-2008: 26th; 23rd; 28th; 21st; 8th; 20th; 3rd; 6th
New Orleans 2002-2008: 27th; 18th; 32nd; 14th; 11th; 26th; 23rd
St. Louis 2002-2008: 13th; 16th; 17th; 30th; 23rd; 21st; 28th

Let’s recap:

– Of the eight dome teams, only three of them have ever finished in the top 10 in total defense since 2002.
– Only two of them (Dallas and Minnesota) have ever finished in the top 5 in total defense since 2002.
– All of them have finished in the bottom half of the league in total defense at least once.
– Atlanta, Detroit, New Orleans and St. Louis haven’t cracked the top 10 in total defense once since 2002.

Granted, there are several huge factors that work against the theory that dome teams are worse off defensively than those that play outdoors. First and foremost, there’s a larger sample size of outdoors teams than dome, so of course they’re going to have better overall defensive rankings. Secondly, 2002 to 2008 might not be a long enough time period to definitively say that dome teams are worse defensively.

But think about it – when has a dome team ever had a consistently good defense? Chicago, Tampa Bay, Pittsburgh, Baltimore, Philadelphia and New England have always been known for their defense. Outside of the “Purple People Eaters” when has a dome team ever been known for its defense? Never. And this plays into the fact that dome teams struggle to make Super Bowl appearances.

Why? It can’t be that these teams have ignored their defenses over the years or have just had terrible luck in the drafts. Free agency has allowed teams to rebuild in just one offseason, so it’s not like these teams haven’t had the opportunity to re-tool their defensive units.

The simple explanation is that teams can obviously move the ball better when they don’t have to deal with weather conditions, so therefore dome teams are more susceptible to giving up more yardage and points. But is that it? So dome teams are just doomed defensively for the end of time? They best they can do on a consistent basis is finish 11-16 in total defense?

Obviously this research is largely incomplete, but it’s an interesting topic.