Week 6 of the 2021 college football season was the wildest and most thrilling yet for an increasingly wild and thrilling campaign. Alabama lost, Oklahoma and Texas played maybe the greatest game in the history of their storied rivalry, Ole Miss and Arkansas lived up to their "most underrated rivalry" status and then some, and the Big Ten got wild after sundown with Iowa outlasting Penn State and Michigan surviving a massive test from Nebraska.
On paper, however, it was a mostly orderly affair. The spread was pretty dialed in on average, and SP+ had its best week of the year from an absolute error perspective -- the absolute-value difference between projection and result. Order on paper and chaos on the field? Sounds pretty perfect! Let's see what the rankings have to say this week.
What is SP+? In a single sentence, it's a tempo- and opponent-adjusted measure of college football efficiency. I created the system at Football Outsiders in 2008, and as my experience with both college football and its stats has grown, I have made quite a few tweaks to the system.
It is, as always, important to note that SP+ is intended to be predictive and forward-facing. It is not a résumé ranking that gives credit for big wins or particularly brave scheduling -- no good predictive system is. It is simply a measure of the most sustainable and predictable aspects of football. If you're lucky or unimpressive in a win, your rating probably will fall. If you're strong and unlucky in a loss, it probably will rise.
The two most consequential movers of the week moved up a combined four spots. First, the combination of Alabama's loss to Texas A&M and Ohio State's third straight torrid performance bumped the Buckeyes ahead of the Crimson Tide for No. 2 overall. If you saw how Ohio State was making a charge on the top two last week, that probably wouldn't surprise you much, but after what we saw through the first few weeks of the season, it's still jarring to see a different top two.
The other move is a little more disturbing to the eyes: 2-3 Wisconsin jumping back up to seventh after beating Illinois.
The current rankings for both Wisconsin (seventh) and unbeaten Iowa (16th) tell us a lot about how SP+ views efficiency and turnovers. The success rate measure -- how frequently you're gaining 50% of your required yardage on first down, 70% on second and 100% on third or fourth -- makes up a healthy portion of the SP+ formula, and Wisconsin dominates Iowa on both sides of the ball.
Success rate (garbage time filtered out): Wisconsin offense 44.7% (53rd in FBS), Iowa 36.2% (119th)
Generally, these efficiency levels are just about the most predictable and sustainable part of football, and Wisconsin clearly has the edge here. But a large reason the Hawkeyes are unbeaten and looking good for the CFP while the Badgers are trying to scrape back to .500 is turnovers.
Turnovers committed: Iowa 5, Wisconsin 14 (11 in losses) Turnovers created: Iowa 20, Wisconsin 3 (1 in losses)
Wisconsin has recovered only 36% of fumbles in its five games, while Iowa has recovered 58% of fumbles in six. Meanwhile, the Hawkeye secondary has turned 42 passes defensed (interceptions plus breakups) into 16 interceptions, while Wisconsin's defense has turned 26 passes defensed into just two picks. Based on national averages for fumble recovery rates and the ratio of INTs to breakups, Wisconsin's turnover margin should be about minus-1.6. It's minus-11. Iowa's should be about plus-6.4. It's plus-15.
Wisconsin quarterback Graham Mertz has been particularly careless with the football, and Iowa's secondary has been utterly brilliant at creating turnover chances. But SP+ sees these teams' turnover margins as unsustainable in two different directions, and as a predictive measure, it sees the Badgers as the more likely team to play at a top-10 level moving forward. It was betting on the Badgers at the beginning of the season, too, and that didn't pay off. Will it pay off over the next two months?
Biggest overall rises
Badgers aside, seven teams made particularly impressive moves, rising by at least 10 spots in the rankings.
San Diego State: up 19 spots from 61st to 42nd
Kentucky: up 15 spots from 45th to 30th
TCU: up 14 spots from 48th to 34th
Baylor: up 13 spots from 36th to 23rd
Syracuse: up 12 spots from 64th to 52nd
SMU: up 11 spots from 55th to 44th
Air Force: up 10 spots from 66th to 56th
There are three unbeaten power conference teams the algorithms have been particularly slow to come around on in 2021: Kentucky, Oklahoma State and Wake Forest. With the Wildcats' brilliant performance against LSU on Saturday, I guess we can say that SP+ is starting to come around on Kentucky. We'll see if that remains the case after next Saturday's trip to Georgia.
Biggest stumbles
Eleven teams moved down at least 10 spots, and if you watched some of them play on Saturday, this probably wouldn't surprise you.
West Virginia: down 22 spots from 40th to 62nd
Virginia Tech: down 16 spots from 33rd to 49th
USC: down 16 spots from 34th to 50th
Middle Tennessee: down 15 spots from 99th to 114th
Texas Tech: down 13 spots from 51st to 64th
Western Michigan: down 13 spots from 70th to 83rd
North Carolina: down 12 spots from ninth to 21st
LSU: down 12 spots from 46th to 58th
Auburn: down 11 spots from 18th to 29th
Maryland: down 11 spots from 21st to 32nd
Memphis: down 10 spots from 69th to 79th
USC has finished 50th or worse in SP+ only once since 1983: It was in 2000, the year before Pete Carroll arrived. Trojans fans better hope that says something positive about their impending coaching search. This program needs a hell of a hire.
