Best defense of 2008: Where does USC rank all-time?

The 2008 USC Trojans were dominant on defense: they shut out three of their opponents, held three more to a field goal, two more to a touchdown, and two more to just 10 points. One of those held to a field goal was Ohio State; Oregon, which finished with the #3 scoring offense in 2008, was held to 10 points.

So where does USC rank all-time? Before the Rose Bowl the commentators remarked that USC was, at that point, the all-time best when their average points allowed was subtracted from the average game score for the year. I'll look at that measure, adjusted for competition of course, in a bit.

First, here are the top ten defenses of 2008:

Top defenses, 2008 football season
#   Team                       record   adj. ave      
 1. Southern Cal                12-1     6.71 [  1]
 2. Florida                     13-1     8.33 [  2]
 3. TCU                         11-2     9.87 [  3]
 4. Ohio State                  10-3    11.88 [  4]
 5. Texas                       12-1    11.89 [  5]
 6. Penn State                  11-2    13.29 [  6]
 7. Iowa                         9-4    13.42 [  7]
 8. Alabama                     12-2    14.70 [  8]
 9. Boise St                    12-1    14.80 [  9]
10. Wake Forest                  8-5    16.37 [ 10]

USC allowed just 6.7 points per game, adjusted for their competition. Their raw average was exactly 9 points per game, up from 7.75 before the bowl game. But they played a tougher-than-average schedule, as does almost every BCS conference team, especially one that goes to a BCS bowl game. Their adjusted average stayed almost exactly the same after the Rose Bowl as holding Penn State to 24 isn't bad at all.

Florida's strong showing against top offense Oklahoma boosted them to #2. #3 TCU held Boise State to 16 points and #4 Ohio State held Texas to 24 points, their lowest total of the year.

#5 Texas and #6 Penn State had solid defenses to go with their offenses; the Nittany Lions' performance against USC didn't affect them much as USC has a top ten offense. #7 Iowa and #10 Wake Forest built their winning seasons on defense as they didn't have nearly as much to offer on offense, while Alabama and Boise State had more but were still defense-oriented teams.

In terms of yardage, TCU ranked slightly better than USC, mainly due to their extremely stingy rushing defense.

Rank Team                         Rec   Total[rank] Rush[rank]  Pass[rank]
  1. TCU                         11-2   201.9[  1]   43.6[  1]  158.2[  5]
  2. Southern Cal                12-1   224.9[  2]   85.8[  6]  139.0[  1]
  3. Florida                     13-1   267.1[  3]   99.2[ 15]  167.9[  8]
  4. Alabama                     12-2   270.5[  4]   71.5[  2]  198.9[ 35]
  5. South Carolina               7-6   284.8[  5]  109.9[ 20]  174.8[ 10]
  6. Tennessee                    5-7   285.4[  6]   99.0[ 14]  186.4[ 21]
  7. Connecticut                  8-5   288.3[  7]  112.3[ 23]  176.0[ 12]
  8. Utah                        13-0   288.7[  8]   91.1[ 11]  197.6[ 34]
  9. Texas                       12-1   292.9[  9]   82.9[  5]  210.0[ 51]
 10. Ohio State                  10-3   293.0[ 10]  112.5[ 25]  180.4[ 14]

The Trojans were second and Florida third, with many of the teams from the scoring defense list joined by South Carolina, Tennessee, and Connecticut.

Back to scoring defense, let's look at how USC ranks for the decade:

Top defenses 2000-2008 seasons (uncorrected for year played)
#   Year Team                  record   adj. ave      
 1. 2000 Florida State           11-2    6.54 [  1]
 2. 2008 Southern Cal            12-1    6.71 [  1]
 3. 2005 Ohio State              10-2    7.26 [  1]
 4. 2001 Miami (Florida)         12-0    7.54 [  1]
 5. 2003 Louisiana State         13-1    7.74 [  1]
 6. 2008 Florida                 13-1    8.33 [  2]
 7. 2004 Southern Cal            13-0    8.80 [  1]
 8. 2002 Kansas State            11-2    9.27 [  1]
 9. 2000 Oklahoma                13-0    9.56 [  2]
10. 2002 Ohio State              14-0    9.61 [  2]

USC ranks #2 among teams from this decade, with Florida coming in at #6. Florida State's 2000 team that lost to Oklahoma in the national championship game. Their raw average was just over 10 points, but they held 11 of their 13 opponents to 14 points or fewer, and faced many of the year's best offenses. Note that two of USC's shutouts were Washington and Washington State and that's what probably gives 2000 FSU the edge.

Let's see what happens if we include all the teams from the 80s and 90s as well:

Top defenses 1980-2008 seasons (uncorrected for year played)
#   Year Team                   record   adj. ave     
 1. 1985 Michigan                10-1-1  1.87 [  1]
 2. 1980 Florida State           10-2    3.13 [  1]
 3. 1991 Miami FL                12-0    3.87 [  1]
 4. 1980 Alabama                 10-2    4.16 [  2]
 5. 1980 Nebraska                10-2    4.17 [  3]
 6. 1991 Washington              12-0    4.56 [  2]
 7. 1983 Miami FL                11-1    4.67 [  1]
 8. 1980 Southern California      8-2-1  4.80 [  4]
 9. 1986 Oklahoma                11-1    4.81 [  1]
10. 1988 Miami FL                11-1    4.84 [  1]

...and the 2008 Trojans have disappeared from the list ; as have the Seminoles and everyone else from this decade. The 1980 Trojans are on the list, though; apparently, 1980 was a really good year for defense, with four teams on the list. Or could that be a result of lower scoring in those days? To correct for rule changes and other things that can boost or quell scoring, we subtract the year's average game score from the team's adjusted average defensive score.

Top offenses 1980-2008 seasons (standardized for year played)
#   year Team              rec    adj. ave    year's ave   difference
1.  1985 Michigan          10-1-1  1.87 [  1]   22.26        20.39
2.  2008 Southern Cal      12-1    6.71 [  1]   26.34        19.63
3.  2000 Florida State     11-2    6.54 [  1]   25.74        19.20
4.  1991 Miami FL          12-0    3.87 [  1]   23.04        19.17
5t  2001 Miami FL          12-0    7.54 [  1]   26.56        19.02
5t  2005 Ohio State        10-2    7.26 [  1]   26.28        19.02
7.  1996 Ohio State        11-1    6.60 [  1]   25.46        18.86
8.  1988 Miami FL          11-1    4.84 [  1]   23.66        18.82
9.  2003 Louisiana State   13-1    7.74 [  1]   26.24        18.50
10. 1991 Washington        12-0    4.56 [  2]   23.04        18.48

This gives a much more balanced view of the relative performance across decades. Michigan's 1985 team still has the best season. In a year when the average score was over 22 points, the Wolverines allowed an incredible 1.87 points when adjusted for competition. They allowed 8.2 points per game in raw numbers, but that included playing Nebraska, Ohio State, and the year's number one offense, Iowa, whom they held to 12 points. Beyond that they had three shutouts and seven opponents held to single digits.

This year's USC places second, a bit ahead of 2000 FSU; the average score this year was about 0.6 points higher than in 2000, pushing USC above the Seminoles as the best defense of the decade. Two undefeated Miami teams, from 1991 and 2001, follow at 4th and 5th, with the latter tied with Ohio State's 2005 squad. Another Buckeye team follows, and then a third Hurricane defense at #8. LSU's BCS title team from 2003 and Washington—the second undefeated team from 1991—rounds out the top ten.

So USC can fairly argue they had the best defense in college football this decade, and over the last 20+ years. If you look from the 1940s on, or even more severely, the 1870s on, the defensive numbers almost become meaningless, with negative averages due to the best teams racking up very high score and garnering 10 or more shutouts, so we'll have to stick the the last few decades.