HuskyPup gets super nerdy on Ole Miss' S&P Unit Rankings
I recently got into a dialogue with someone regarding Ole Miss's rush defense. I was arguing that the LSU and Auburn games were unsurprising, as Ole Miss was 116th in ypc (yards per carry) allowed.
However, as many have noticed, Ole Miss is actually ranked 56th in rushing defense by S&P+. That means they are ranked better than approximately 60 teams that hold opponents to fewer ypc. The quick answer here is "well, maybe it's the strength of their schedule?" But that doesn't really hold water either. Here's an example:
- Missouri and Ole Miss have two common opponents: UGA and LSU
- Missouri gave up 2.66 ypc and 8.04 ypc, respectively
- Ole Miss gave up 5.23 ypc and 8.64 ypc, respectively
- S&P+ has Ole Miss 56th in rush defense and Missouri 98th, even though Ole Miss was significantly worse in ypc allowed against common opponents.
The next question is: how and why is Ole Miss then ranked -so- far ahead of Missouri, even with worse statistics? First, you have to understand why it's called S&P+. S&P is so-named because it takes into account Success Rates and Points Per Play. The '+' comes because it takes into account opponent strength.
Ole Miss's Rush defense is an abysmal 113th in IsoPPP, meaning that they give up a very high number of points through explosive plays (opponent yardage tends to generate points). They are also 85th in success rate, meaning opponents often get the yardage they need on a given down. That averages to 99th. Missouri is 96th and 108th in both categories, averaging to 102nd. Since this still doesn't explain why Ole Miss is 56th and Missouri is 98th in rush defense, we must delve further.
There are 4 minor rankings for rush defense: Adj. Line Yards, Power Success Rate, Stuff Rate, and Opportunity Rate. Here, we finally see why Ole Miss may be ranked so much higher, as they are ranked 38th, 52nd, 56th, and 97th. Missouri is ranked 76th, 114th, 82nd, and 107th. Now we can see a difference between the teams. But what do these rankings mean, and why are they so different?
These rankings all relate to plays made at-or-near the line of scrimmage. Adj. Line yards weights the first four yards gained on a run most heavily, and throws out any yardage beyond 11 yards. The idea here is that the front seven isn't really responsible for anything that happens 10 yards downfield. Power success rate and stuff rate are similar, they look at the ability of the team to prevent an opponent from converting a 3rd and 2 and their ability to get TFLs or stop a play for a short gain.
Ole Miss is actually pretty decent in short yardage, because the defensive line is solid. While the statistics are falling off due to depth issues, they have a solid 19.7% chance of stuffing a run at the LOS. Missouri, on the other hand, is notably worse - most carries against Missouri's defense are going to gain positive yardage. While Football Outsiders does not publish exactly how S&P+ formulates its overall rating from the underlying stats, I believe this is why Ole Miss is ranked so much higher than Missouri.
However, this ranking is likely meaningless. While Ole Miss may be good at stopping you at the LOS, their issue is that they are still 113th in IsoPPP. Why? Because any plays that /do/ get beyond their defensive line have generated massive yardage. Against Ole Miss, Fournette had 16 carries. Half went for 5 yards or less (1.37 ypc). The other half were all 7 yards or more (for an eye-popping 34.12 ypc). Simply put, their back 7 is truly terrible in run support, frequently completely missing their gap assignments and whiffing on tackles, and is probably among the very worst in football. Who really cares that they can stop Fournette for a one yard loss on one carry only to give up a 59-yard touchdown run the next (that actually happened)? On defense, one bad play will negate many good ones, so explosive plays are extremely detrimental (see UF against UT, where blanket coverage on 80% of their plays was rendered meaningless by huge coverage busts).
Ole Miss's Rush defense is an abysmal 113th in IsoPPP
In conclusion, Ole Miss is likely ranked better in S&P+'s rush defense rankings because they hold backs to a substantial number of minimal gains. However, for every good player there's a far worse bad play, which is why they average out to 116th nationally in per/carry averages. I have a tremendous amount of respect for Bill Connelly and what he does, and no model is perfect. In this instance, Ole Miss is simply so bad in one area (run support by the back 7) that they break the model. This is why, as great as advanced stats are, you need to understand them in order to apply them in a meaningful way when analyzing a team.