Can someone give me a quick overview of what these numbers mean? I'm not familiar with the F+ ratings/rankings.
Well first of all I should post a link to Football Outsiders, who puts these together.
And F+ is in fact a mashup of Bill Connelly's SP+ and Brian Fremeau's FEI, two different stathead rankings that are slightly different from one another. Which is good, incorporating multiple perspectives makes things more robust.
But the basic idea is looking at per play and per possession efficiency, adjusted for schedule strength and home/road, and tossing out garbage time possessions. So basically, how well are you able to move the ball and prevent the ball being moved, relative to the difficulty of the games you're playing?
So it's even a little more under the hood than something like KenPom in basketball which is (I believe, correct me if I'm wrong) derived entirely from just what the final score is, then adjusted for opponent quality and location. F+ gets a little deeper into how well you actually play.
It's the gold standard for college football. (Football Outsiders is also the gold standard for NFL analytics if you're into that). It knows when you laid an egg and had to struggle to beat a bad cupcake. It knows when you gave a great team a really difficult fight.
I think it's something like how much better or worse you are than the middle/average team. So + is better than average, - is worse. Higher number is farther from average.
Oh, yeah, the actual percentages are the deviation from the average team.
Or at least they were, they've changed the units for 2020 which is very annoying and makes apples-to-apples comparisons impossible. The rankings 1-120something work fine enough, but obviously that "average" is a little different every year (I believe Bill Cubit's interim team won the coveted "F+ Closest to FBS Average Team" trophy)