— -- There is no argument over which defense is the best in college football this season. Zero. Zilch. None.
The Alabama Crimson Tide lead the country in points per game, yards per game, yards per play, Total QBR and, well, just about every other major defensive category this season.
But the question still remains: Is this the best Bama defense Nick Saban has ever coached? Entering this season, most would have agreed that Alabama's top defense under Saban was the 2011 national championship-winning squad. That team allowed only nine offensive touchdowns and has been widely regarded as one of the best defenses in college football history.
So how do the two compare?
Based on traditional statistics, Alabama's 2016 defense does not compare to its 2011 team. The 2011 unit -- led by top-35 NFL draft picks Dont'a Hightower, Courtney Upshaw, Mark Barron and Dre Kirkpatrick -- allowed the fewest points per game and yards per game of any defense in the past 25 seasons. And their season totals blow away the marks set by this year's Alabama squad.
Notable Alabama Defenses Under Nick Saban
(best in a season since 1988 Auburn allowed 7.2 PPG)
2016 11.4 PPG
Yards per game
2011: 183.6 YPG
(fewest allowed in a season since 1986 Oklahoma allowed 169.6 YPG)
2016: 244.0 YPG
Yards per play
2011: 3.3 YPP
2016: 3.9 YPP
But sometimes base-level stats can be misleading. For example, the yardage totals do not account for the significant impact of turnovers (and subsequent defensive touchdowns). They also do not account for the strength of offenses faced or the context of when the yards came.
Digging deeper into advanced stats -- which account for all of those factors and more -- tells a different story. The 2016 Alabama defense is the top unit of the past decade by defensive efficiency -- and it's not even close!
ESPN's defensive efficiency ratings capture a defense's per-play contribution to the team's scoring margin, adjusting for opposing offenses faced. These ratings are built off the framework of expected points added (EPA), which accounts for the context (down, distance, yard line, etc.) of every play by measuring the change in a team's scoring potential from one play to the next. If a defense stops a team on third down (no matter how many yards are gained), forces a turnover or stymies an offense in the red zone, it generally results in negative EPA for the offense and positive EPA for the defense.
While the explanation of the statistic may be complex, the rationale behind it is intuitive. Good defensive plays result in high defensive EPA, and over the course of the season, the best defensive teams almost always end up leading the country in this category. Defensive efficiency takes this statistic a step further and adjusts for pace, the strength of opposing units faced, and blowout situations. It is expressed on a 0-to-100 scale (50 is average) for easier understanding.
Alabama leads the country in defensive efficiency by nearly 10 points this season, and is on pace to end the season with by far the top mark of any team in the past decade.
Highest single-season defensive efficiency, past 10 seasons
1. 2016 Alabama: 98.2 (on a 0-to-100 scale)
2. 2011 Alabama: 94.5
3. 2014 Clemson: 92.5
4. 2015 Alabama: 91.6
5. 2012 Alabama: 91.2
Why is Alabama's 2016 squad rated so much higher than its vaunted 2011 unit? Below are three reasons that are likely lost in the traditional, base-level numbers.