Was the 2015 Denver Broncos defense the greatest defense in NFL history?

As the 2015 season wore on, particularly into the playoffs, the Denver Broncos defense began to get mention as being historically great. The Broncos piled up win after win, with game-changing plays from the defense, and seemingly little help from their offense. Their secondary was nicknamed "The No Fly Zone," and the legend of the the defense grew. After their dominating performance in the Super Bowl, there was even talk of them being the greatest ever. Safety T.J. Ward said in July that the Broncos defense "can become the greatest of all time."

We live in an attention-grabbing, social media-driven world , where proclamations are Tweeted out by millions of "experts" mid-performance. Perhaps now that the dust has settled on the 2015 season, we can gain some perspective. Before the new season kicks off I want to take a look at the 2015 Broncos defense to see just how good they were. I figure the best way to do that is to compare them to a relatively recent defense that is generally regarded as one of the best, that being the 2000 Baltimore Ravens. I also want to include another team that, although known as having a great defense, may not be considered in the same category as the Ravens: the 2008 Pittsburgh Steelers. I will compare the teams statistically, and then take a look at some of the reasons why each team's defense may be considered better, or "not as great" than they actually were.

For the comparison, I chose 20 statistical categories that most fans will be familiar with. I feel it should offer a broad enough range of defensive statistics to result in a valid analysis.

Before we get to the numbers, I want to explain what I did to account for the different "eras" each team played in. For any comparison such as this, we can't just use the raw numbers. The offenses of 2015 are much more difficult to stop than the ones of 2000, or even 2008. What I did to adjust for that is compare each teams' numbers with the NFL average. For example, if Team A allows 250 points in a league where the average team allows 300, they allowed .833 of the average. If Team B allows 200 points where the average team allows 150, they allowed 1.33 of the average. So, in our example, even though the raw numbers show Team B allowing fewer points, they were 33% worse than average, where as Team A was 17% better than average.

For each category, I will list where the team ranked for that season, followed by their comparison to the NFL average, listed as a decimal (as in our example). The leader among the 3 teams (as compared to their respective season average) will be listed in bold.

Total Defense		'15 Broncos	'08 Steelers	'00 Ravens
Points Allowed		4th/.811	1st/.633	1st/.499
Yards		1st/.803	1st/.725	2nd/.776
Yards/Play		1st/.80	1st/.736	2nd/.843
Turnovers		8th/1.16	9th/1.17	1st/1.63
1st Downs		1st./.824	3rd/.719	1st/.602
Pass Defense
Cmp. %		8th/.952	5th/.926	10th/.960
Yards		1st/.803	1st/.743	8th/.966
TD		5th/.722	3rd/.594	2nd/.537
TD%		4th/.717	3rd/.590	2nd/.538
INT		13th/1.03	6th/1.38	5th/1.35
INT%		15th/1.0	5th/1.36	4th/1.22
YARDS/ATT		1st/.849	1st/.783	4th/.896
ADJYARDS/ATT		3rd/.803	1st/.631	2nd/.738
YARDS/CMP		1st/.896	1st/.833	6th/.947
QBRATING		4th/.891	2nd/.778	3rd/.820
SACKS		1st/1.40	2nd/1.57	23rd/.881
SACK%		1st/1.36	2nd/1.47	23rd/.886
Run Defense
Yards		3rd/.768	2nd/.692	1st/.539
YARDS/ATT		1st/.805	2nd/.786	1st/.659
TD		15th/.877	3rd/.470	1st/.376

The 2015 Broncos finished 1st in this comparison in zero of the 20 categories. They did finish 2nd 7 times. The Ravens were 1st in 8 of the categories, 5 times placing second. The Steelers were 1st 12 times, finishing 2nd 8 times. For illustrative purposes, and to commemorate the current Olympic Games, let's do a Medal Count:

	GOLD	SILVER	BRONZE
'08 Steelers	12	8	0
'00 Ravens	8	5	7
'15 Broncos	0	7	13

First off, the Broncos "finishing last" in this comparison should not be taken to mean they were not a great defense. This is stiff competition. We are however, considering the Broncos for inclusion in the "All-Time Great" defenses. Not leading in even one of the categories certainly doesn't help their cause.

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We've taken into account the difference in the offensive proficiency between the "eras" each of the 3 teams played in. Another thing that might play a difference in the statistics is the "quality" of offenses each team faced; the "difficulty of schedule concerning offense only," if you will. In the real world (on the football field), that does't make a bit of difference. You have to beat whoever is in front of you, with no excuses either way. For the purposes of our discussion, it's worth taking a look at.

What I did was take each team's opponents and find the "average offensive rank (of 32 teams)" for Points and Yards. The 2000 Ravens played in a 31 team league. I adjusted their numbers for a 32-team league. In this analysis, the "lower the number" of your opponent, the better they were offensively; meaning it would be more difficult for the defense.

The toughest schedule you could face, by offensive rank, in theory, is a "6". You couldn't get a "1" as you could only face the #1 ranked offense twice (if they were in the same division). Same for the #2, and #3 offense. After that, you could face the #4, #5, and so on.

Conversely, the "easiest" schedule, by offensive rank would be a "27" (26.93, to be exact). Alright, let's see how tough the opposing offenses were for each of our 3 teams:

AVG OPPONENT OFFENSIVE RANK (OF 32 TEAMS)
		'15 Broncos	'08 Steelers	'00 Ravens
POINTS		16.8	17.54	21.54
Bottom 1/4 teams faced		4	5	7
top 1/4 teams faced		3	4	0
YARDS		18.98	16.67	20.89
Bottom 1/4 teams faced		5	4	7
top 1/4 teams faced		2	3	2

In terms of points scored, it seems the '15 Broncos faced slightly tougher offenses than the '08 Steelers. In yardage gained, the Steelers faced tougher opposition. The '00 Ravens would seem to have benefited, at least by this measure, from facing relatively weaker offenses. Notice that the Ravens faced 7 teams that finished in the bottom 25% for both points scored and yards gained. They also did not face any team that finished in the top 25% of offenses for points scored. The Broncos and Steelers faced relatively similar competition, all things considered.

For the sake of comparison, I will adjust the '15 Broncos and '08 Steelers for the % difference in offenses faced for both points allowed and yards allowed:

ADJ FOR OPPONENTS OFFENSE		'15 Broncos	'08 Steelers	'00 Ravens
Points Allowed		1st/.637	1st/.517	1st/.499
Yards		1st.733	1st/.586	2nd/.776

The adjustment does bring the Broncos to 2nd in yards allowed instead of 3rd. Of course, it brings both the Broncos and Steelers closer to the Ravens number for points (a record for a 16 game season).

Again, this "adjustment" is not anything I've seen done before. It only serves here to give more context to the discussion of these great defenses.

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One talking point put forward in the proposition of the'15 Broncos having one of the best defenses ever is that they got little help from their offense. The same consensus is generally held when discussing the '00 Ravens. While I'm not going to be as exhaustive in the list of offensive statistical categories, it is still prudent to compare each of our 3 teams' offenses in a few basic ones that are used to rank offenses. I will use Points and Yards. I also added Turnovers, since they can have an impact on the number of points allowed.

OFFENSIVE RANK		'15 Broncos	'08 Steelers	'00 Ravens
POINTS		19	20	14
YARDS		16	22	16
TURNOVERS		29	15	9

Several interesting takes from the data:

-Of the 3 teams, the '00 Ravens had the best offense, on all counts.

-The Steelers had the worst offense, with the exception of turnovers.

I don't have any idea how to weight each of those categories. The Broncos were near the very bottom of the league when it came to turning the ball over. How does that, combined with them being slightly better than the Steelers in terms of yards and points. compare? Good question. We will have to leave that one alone for now. Suffice to say that the '00 Ravens were not as putrid on offense as everyone's perception of them would seem to indicate.

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Lets's take a deeper look at perceptions.

All perception is, in this context, is a mental impression of something. Perceptions are useful. It's a tool we use to compress many pieces of information into an easily understandable, retrievable, file, if you will. Our perceptions are not without flaw, however. They are also powerfully influenced by chronology, meaning the most recent event will likely have the most significant impact on our senses, and color our perception accordingly.

The perception of the 2000 Ravens offense is forever linked to Trent Dilfer's (Tony Banks started as many games during the regular season) mediocrity and Jamal Lewis pounding the ball on the ground. That image is locked in our minds and can't be changed.

Just as the image of the 2015 Broncos offense is one of an inept Peyton Manning being benched mid way through the season for an unproven Brock Osweiler. Manning has since retired and Osweiler left via free agency. We are not going to remember the 2015 Denver Broncos offense in any other way than mediocre.

The perception of the 2008 Steelers offense, however, is still being written. Ben Roethlisberger was the quarterback of that team, and is still playing today. Ben is playing at a high level currently. That was not the case in 2008. The offensive line of the current Steelers team boasts two All-Pro players (Pouncey and Decastro), and is a strength of the team. The 2008 O-line was shaky at best, allowing Roethlisberger to be sacked 46 times during that season. When many fans think back on the 2008 Steelers and their QB, it can be difficult to separate "2008 Ben" from "2015 Ben."

Beyond the perception of the offenses of each team, what is the image that comes to mind when fans think of each Super Bowl? This is key to our discussion as the Super Bowl is the last, defining moment for each team, and will cement the perception of them for everyone.

For the 2000 Ravens, I think of them surrendering only 7 points to the Giants, and that coming via kickoff return. Then the ensuing return by Jermaine Lewis of the Ravens to effectively end that game. So the Ravens defense didn't allow a score, showing how dominant they were. The Ravens special teams put the game away, showing they scored without help from their offense. Ray Lewis had a good (not great) game and was named MVP.

For the 2015 Broncos, it begins with Von Miller's strip sack of Cam Newton, which brought the first TD of the game. It ends with another strip sack by Miller, which effectively put the game away. In between, Peyton Manning turned the ball over twice, was sacked 5 times, and the Broncos offense was not asked to win the game. Von Miller was named MVP.

For the 2008 Steelers, it's Ben Roethlisberger leading the Steelers on a last minute, game-winning drive. It's Santonio Holmes making a stupendous catch for the game-winning TD. Yes, many will remember James Harrison's amazing 100 yard interception return. However, Santonio Holmes was named MVP.

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I went into this exercise attempting to find out if the 2015 Denver Broncos defense deserved the lofty claims bestowed upon them. I also attempted to discern the source of their perceived greatness. I did this, as I tend to, with as much fact based, statistical analysis, as was practically reasonable to do. I came away with more than that.

I believe I've shown that although the Broncos defense was great, and no doubt the #1 reason they won the Super Bowl, they are not quite in the historically great category.

We can understand why the perception of the 2015 Broncos defense, as well as the 2000 Ravens defense, is colored by not only the perception of each team's offense, but also by how they looked in their last game (Super Bowl). The same, of course, holds true for the 2008 Steelers, although those perceptions seem to elevate the Broncos and Ravens defense(s) and diminish, slightly, the Steelers defense.

I also am left with an even greater understanding of just how dominant the 2008 Steelers defense was. I watched every game that season, and certainly saw with my own eyes the brutal destruction they wrought on their opponents week after week. The 2008 Steelers didn't have a catchy nickname (such as the Steel Curtain of the '70's, or Blitzburgh of the '90's) to help cement their legacy. Nobody dismisses that Steelers defense as not great. The perception of that team is colored somewhat by their last game, however, and the offense "winning it" for them.

Not only am I 100% confident the 2015 Broncos defense is not in the same category as the 2000 Ravens, I feel a strong case can be made that these guys...

...were every bit as good as that Ravens defense, if not better.

No nickname required.