Much has been made about domes and stadiums with retractable roofs that can be closed whenever the weather is less than desirable.  Common thinking suggests that playing indoors provides a huge advantage to offenses while naturally putting defenses at somewhat of a disadvantage. 

The idea is that being shielded from cold, rain, wind, and snow creates a pristine environment that inherently favors offense over defense.  But is this commonly held belief actually true?  What do the numbers say?

I will admit that at first glance, the case seems quite compelling for advocates of this idea.  Quarterbacks from indoor and outdoor teams alike both seem to fare much better indoors than outdoors. 

Indoor quarterbacks have a striking disparity between home and away games, while outdoor quarterbacks tend to demonstrate far greater consistency, some even doing better away than at home.  But is that all there is to it?  Or is there a better explanation for the phenomenon? 

I will investigate this issue by using two prime candidates for each type of home venue, the Colts and the Patriots.  The Colts are well-known for the comforts of their previous home, the RCA Dome, and their current home, Lucas Oil Stadium, and its retractable roof. 

The Patriots play their home games outdoors in bitter New England weather at Gillette Stadium.  It’s not exactly Lambeau Field, but certainly comparing quarterbacks Tom Brady and Peyton Manning makes for a compelling story.

Since poor weather is the offered as reason for why offenses are presumably at an advantage over the defenses they face indoors, let’s start by looking at how Tom Brady has fared in various weather conditions. 

Brady has a career rating of 89.8 in cold weather games (21-40 F) and a career rating of 93.8 in mild weather games (41-60 F).  That certainly seems like an indication that cold hurts Brady and thus offense in general, but then again Brady’s career rating in warm weather games (61-80 F) is 86.1. 

Looking at YPA (yards per attempt) tells a similar story.  Brady has a career average YPA of 7.2 in both cold and mild weather games and a career average YPA of 6.8 in warm weather games.

If we were to conclude that cold weather hurt Brady based on these numbers, we’d have to conclude even more so that warm weather hurt Brady.

Windy games tell a similar story.  Brady has a career average rating of 89.7 and a career average YPA of 7.0 in windy games. Both are below his warm weather numbers.  Games with precipitation (rain or snow) do signal a drop in Brady’s rating (83.5), but they also give Brady a higher YPA (7.3) than cold, mild, warm, or windy games. 

At any rate, with only 10 precipitation games in his career, this category cannot offer us very much in the way of a reasonable sample and certainly does not have a tremendous affect on Brady’s overall career numbers.

Peyton Manning’s more limited sample of outdoor games in various weather conditions tells a similar story.  His career average rating in cold weather games (86.9) is higher than his career average rating in mild weather games (83.0). 

His career average YPA in cold weather games (7.7) is higher than in mild (6.9) or warm (7.3) weather games. 

In fact, Manning’s career 83.0 career rating in mild weather games is lower than his 83.1 career rating in windy games and 84.1 rating in precipitation games.   His mild weather career average for YPA (6.9) is actually lower than in precipitation games (7.0) and only marginally higher than in windy games (6.8). 

It should be noted that Peyton Manning has only played in 6 career precipitation games and 10 career cold weather games.  Obviously the small samples found with both quarterbacks in each situation create large margins of error that render virtually all these differences insignificant.

So if it’s not exactly the weather, then what is it?  While Manning has fared fairly consistently in various forms of outdoor weather, his numbers are clearly better indoors (100.4 rating and 8.0 YPA). 

The same can be said for Tom Brady in his more limited set of 10 indoor games (104.7 rating and 8.3 YPA).  Those numbers alone tell us that something is going on.

Tom Brady is the simpler of the two to answer, so let’s start with him.  Brady has played in 10 indoor games in his career—though really only nine since one came in his rookie season with only two pass attempts. 

Of those nine real games, five came against defenses ranked 26th or worse in opponent quarterback rating allowed.  Only two out of those nine games came against defenses ranked above average in opponent quarterback rating allowed (fifth and third). 

One of those two defenses, the Minnesota Vikings in 2006, ranked only average or poor in two other important passing categories.  The Vikings tied for last in the league in passing yards allowed and tied for 12th with three other teams in YPA allowed. 

The other one of those two defenses, the Indianapolis Colts in 2007, forced 25 percent of Brady’s interceptions in that season and gave him one of his worst rated games all season long.  His 95.2 rating in that game was still impressive by his career standards, but it was well below his 117.2 rating on the season.

Did Brady just get lucky with so many weak pass defenses?  Well, not exactly.  You see indoor teams tend to build for offense instead of defense. 

Take a moment to think of some indoor teams across the league and see if that sounds about right to you.  Obviously, quarterbacks are expected to do better against weaker defenses than they are against average or stronger ones. 

Take the 2008 season for example.  Of the 9 teams who play at home in a dome or retractable-roof stadium, not a single one cracked the top 10 in opponent quarterback rating allowed. 

Five of the nine teams did make the bottom 10 however.  The average ranking in 2008 for these indoor teams was 22.6.  Some would take this as evidence that indoor venues do put defenses at an inherent disadvantage, but I will address that idea more directly later in the article.

With all that said about weaker indoor defenses, Brady interestingly enough actually wound up with a lower indoor than outdoor rating in three of his seven seasons as a starter (encompassing four out of the nine indoor games).

The real reason why Tom Brady’s career indoor rating is so much higher is not because he has always done better indoors but because of three monster games, two of which came back in 2001 against 28th and 30th ranked defenses (opponent quarterback rating). 

Tom Brady did put up one of those huge games (140.4) against a 17th ranked Falcons pass defense in 2005, but he also recorded a 67.4 rated game against the 30th ranked Lions defense back in 2002.

If you look at it from the perspective of season by season and game by game, the presumed indoor advantage, even against weaker defenses, doesn’t look quite so compelling after all with the Tom Brady example.

Obviously weaker indoor defenses don’t quite explain Peyton Manning’s significantly higher rating indoors since he plays the majority of his indoor games at home against all types of defenses across the league. 

However, it is with an indoor quarterback like Peyton Manning that we can finally get to the heart of the matter and determine if playing indoors really benefits offense over defense.

It’s clear that Peyton Manning does better at home indoors than he does away outdoors.  However, if we were to take this as evidence that playing indoors inherently favors offense over defense, then we would expect to see the Colts defense struggle more at home in those same supposedly anti-defense conditions. 

I was able to pull together the points scored and allowed by the Colts at home and away in Peyton Manning’s career.  The Colts scored 27.1 points per game indoors at home and 25.0 points per game away.  On the other hand, the Colts gave up 19.4 points per game indoors at home and 23.3 points per game away.

So it turns out that not only does the Colts defense do better at home indoors, but that it does dramatically better, and much more so than the Colts offense.  The Colts gave up 3.9 fewer points per game at home while the Colts scored only 2.1 additional points per game. 

That’s nearly twice the difference for the defense.  That’s a 20.6 percent change for the defense compared to a 7.7% change for the offense: more than 2.5 times the rate of change.

Since homefield is supposed to be an advantage for a defense regardless of venue because of issues like crowd noise, we can can control for the homefield aspect of indoor games for the Colts by looking at indoor games played on the road.

Unfortunately, that produces a very small sample similar to Brady's indoor sample.  Regardless, the Colts gave up an average of 23.4 points in outdoor road games and an average of 22.7 points in indoor road games.

That's not as big of a difference as seen when comparing home and away games, but the Colts defense still did better indoors than outdoors even when throwing out home games.

More important than the Colts having given up fewer points away indoors than away outdoors though is the fact that they did not give up more points. If playing indoors really did put defenses at an inherent disadvantage, then you would expect the Colts to give up more points in indoor away games than outdoor away games, not less.

In case anyone is wondering, I checked the points scored rankings of the opposing offenses in this small sample and saw that they came out average overall.  In that regard the sample is representative though most of those games came against the same division-rival Houston Texans.

Obviously the Colts defense is not at a disadvantage indoors, and clearly it is the Colts team as a whole that is at an advantage indoors, not specifically the offense.  Why?  Well, because while playing indoors does not favor offense over defense, it does favor speed over size. 

Turf enhances speed and thus favors teams built for speed over those built for size.  On the other hand, poor muddy field conditions neutralize speed and thus favor teams built for size over those built for speed.  Simply put, teams built to play indoors are at an advantage indoors and teams built to play outdoors are at an advantage outdoors.

If you are having a difficult time trying to understand how a defense could possibly benefit from playing indoors, consider the Colts defense as the perfect example.  Would the Colts speedy edge rushers be at a greater advantage playing somewhere where their speed is enhanced or neutralized? 

I’ve heard games played in Indianapolis referred to as track meets for Dwight Freeney and Robert Mathis.  They get that extra burst off the snap, but do those opposing offensive linemen really back peddle any faster while trying to block them?

Similarly, the Colts undersized but speedy linebacker core can flow to the ball and gang tackle more efficiently with enhanced speed on turf to account for what they give up in size.  Little Bob Sanders gets that much more velocity behind the wallop he packs from the secondary with that turf underneath him.

So why are indoor teams (and thus their quarterbacks) so less consistent than outdoor teams at home and away if both play best in the situation for which they were built?  The answer is not really so hard to find if you think about it: more than two-thirds of the teams in the league call outdoor venues home. 

This means that when an indoor team plays at home, it is more often than not playing against an outdoor team that was not built to play indoors.  On the other hand, when the same indoor team plays away, it is mostly likely playing outdoors against a team built to play outdoors. 

Conversely, outdoor teams, whether at home or away, are more often than not playing outdoors against another team that is also built to play outdoors.

If you’re having trouble seeing what overall team performance has to do with individual quarterback ratings, consider the most dramatic splits for Manning and Brady. 

Brady has a career average rating of 101.3 in wins, but he has a career average rating of 65.1 in losses.  Similarly Manning has a career average rating of 105.0 in wins but a career average rating of 77.1 in losses.