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Ranking Defenses Based on Difference Compared to Average
Offense and defense rankings based on total numbers and straight averages can be misleading at times. If a team plays opponents with strong rush offense but weak pass offense, the team's pass defense stats might look better than what they really should be. This is something Michigan was being accused of due to the fact that much of our "bad" defensive games came against strong rushing teams (Alabama and Air Force).
One way to mitigate this "effect" would be to not look at the totals and average numbers, but compare the game output against the average output the opponent has produced against all opponents. This produces numbers that show you how good your performance was compared to all other team that your opponent has played. It is more useful comparative method than using just total numbers.
So, exactly how does it work?
Here are the stats for Michigan so far this year:
|Opponents||Rush Net Total||Pass Yds Total||Total Yds||Pts||Avg Rush Total||Avg Pass Total||Avg Total Offense||Avg Scoring Offense|
|Average All Opp||145.1||145.9||291.0||17.3||196.0||194.7||390.7||27.5|
|Opponents||Avg Rush Off Diff||Avg Pass Off Diff||Avg Total Off Diff||Avg Scoring Off Diff|
|Average All Opp||-24%||-24%||-26%||-39%|
The first four columns of stats represent the actual stats from the game played against Michigan. The second set (of four) columns are the average output of that team against all opponents this year. The
last set (of four) columns second table are the differences in percentage of actual game stat versus the total year averages.
As you can see from the table, Alabama produced their average offensive output against Michigan while Purdue and Illinois barely produced about half of their normal offensive output.
By averaging all of the averages, we find that our defense is reducing our opponents' normal offensive output by about 25%, while only allowing only 61% of their normal scoring output.
Sounds pretty good, but how does that compare to rest of NCAA?
I didn't have enough time to calculate the differential averages for every team in NCAA, but I did the analysis for top 10 Pass/Rush/Total defensive teams and all of Big Ten (plus ND). I did not include stats against FCS opponents. Here it is ranked by total offense differential.
Few things that stand out:
- Alabama, LSU, and Florida St defense stand above the rest
- Michigan and Michigan St defenses stand above the rest of B1G
- Michigan is pretty good at both run and pass defense
- Ohio St pass defense is HORRIBLE!
- BYU defense is much better than I thought
- Many of the defenses highly ranked in one (pass or rush) only because they are so horrible at the other (I am looking at you Arizona St, Stanford, Nebraska and Oregon St!)
- Notre Dame is living on borrowed time - their scoring differential is MUCH higher than what rest of the defensive differentials would indicate
I do believe converting straight up numbers to percentages makes it much easier to compare between pass/rush and between different teams. I hope most of you find this useful. If I get enough upvotes, I will do the same analysis for offense as well.