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Getting Disruptive, Part Deux

Time to revisit something KJ first investigated a couple weeks ago: the rate at which Michigan State's defense disrupts the opposing offense's rhythm.  To briefly review:

The goal of any football defense, then, has to be to disrupt the opposing offense's rhythm, with the goal of creating a situation where picking up 3-5 yards per play isn't enough to keep a drive going.

Looking at the statistics available to us, there are four quantitative indicators of a defense's ability to disrupt the opposing offense.  In ascending order of disruptiveness:

  • Quarterback hurries: Increasing the odds the offense will throw an incomplete pass and lose an opportunity to gain yardage
  • Tackles for loss: Increasing the yardage the offense has to gain to achieve a first down by sacking the quarterback or stopping a running play for a loss
  • Forced fumbles: Creating the opportunity to recover a fumble and end the opponent's offensive possession
  • Interceptions: Definitively ending the opponent's offensive possession
(If specific stats on penalties by the opposing offense--holding, etc.--were readily available, I'd include those, as well.  Also, I'm defining "forced fumble" liberally, counting any fumble by the offense, even if it's not directly attributable to a defensive player.)

With the goal of creating a nifty new statistic, we can start by summing these four numbers.  There's some double counting involved (a sack can result in a forced fumble, a quarterback hurry can result in an interception), but those instances tend to place more weight on turnover-inducing plays, which is fine.  The summed number is then divided by the number of plays run by the opposing offense (tempo-free!) to arrive at a number we'll call Disruption Percentage.

This time around, we're also including pass breakups in the equation, as it seems to belong: it's another type of affirmative play by the defense that has a negative effect on the offense's performance and tempo/rhythm.

In any event, here's how we're doing:

Montana St 5 2 4 0 0 11 54 20.4
Central Mich 0 4 6 0 1 11 76 14.5
Notre Dame 1 3 4 1 1 10 71 14.1
Wisconsin 4 2 3 1 0 10 81 12.3
Michigan 1 3 10 3 1 18 60 30.0
Illinois 6 3 8 0 1 18 60 30.0
Northwestern 2 2 6 3 0 13 76 17.1
Iowa 0 4 5 0 0 9 66 13.6
Minnesota 0 1 5 1 1 8 73 10.9
TOTAL 19 24 51 9 5 108 617 17.5


(Editor's caveat: You'll notice that we had no quarterback hurries and only one pass breakup against Minnesota.  That could very well be accurate, but those two statistics--hurries and breakups--are also undoubtedly the weak part of this analysis: they're highly subjective statistics, and without doing our own UFR-style review of the game, we're essentially at the mercy of the particular official statistician on duty that week.  I definitely don't think that it's a reason to discount the analysis entirely, but it's something to bear in mind.)

Eh, not so good.  The last time we ran this analysis--after the Northwestern game--KJ was pleased to note that our defense's disruption percentages were trending positively.  Well, since then, that's certainly come crashing down.  It probably comes as very little surprise to MSU fans that two of the three least disruptive defensive performances have come in the past two weeks.  Iowa was somewhat predictable, as that's a team that will, ideally, play a conservative offensive game because their defense is so good.  Of course, that's not exactly how things have worked out this season for them: one or two of the third quarter STANZIBALLS against Indiana would have been, uh, enormously useful in our game.  Our complete failure to hurry the quarterback against Iowa probably cost us our chance at one or two easy interceptions.  And the Minnesota game . . . well, we all knew that Saturday night was our worst defensive performance of the season, and these statistics certainly buttress that feeling.

So, a few concluding thoughts:

  • The Michigan and Illinois games increasingly look like statistical outliers; that's not surprising, of course, as they seem to be two of the three worst teams in the conference.
  • It also seems that, even more than the play of the secondary, the real key to success for our defense is getting a consistent pass rush.  In our three conference wins, our pass rush statistics look like this:

    Michigan 4 1
    Illinois 6 6
    Northwestern 4 2

    And in the three losses:

    Wisconsin 0 4
    Iowa 2 0
    Minnesota 2 0

    Again, not conclusive, but there's definitely a trend.  It's clear that our secondary just isn't very good in coverage; when opposing quarterbacks have time to throw the ball, they tend to pick us apart.  When we're able to pressure the quarterback, we at least have a fighting chance.
  • Finally, it's impossible to overlook that we've only forced 14 turnovers through 9 games.  That's a little over one and a half per game--a good turnover margin, but an absolutely awful turnovers forced figure.  Making big plays from time to time can cover up some glaring defensive weaknesses; we clearly have weaknesses, but haven't shown the ability to force the turnovers needed to mitigate the deficiencies.

Looking ahead, we face three average-to-decent offensive teams to close the season: in terms of offensive efficiency (adjusted for schedule strength), Western Michigan ranks 62nd in the country, Purdue ranks 43rd, and Penn State ranks 17th.  Given that our margin of error is essentially zero if we want to play in a bowl game, it would certainly behoove our coordinators to make some changes on defense to improve the pass rush and create more big plays.  It appears that our basic 4-3 set is no longer confusing anyone.