College football SP+ rankings after Week 4

Through four weeks of the 2021 college football season, only two teams have genuinely separated themselves from the riff-raff. Georgia and Alabama have been awesome, each beating top-10 teams away from home and destroying everyone else. Lots of other teams have looked the part once, maybe twice, but outside of the top two, the more we see of the FBS field, the less it feels we know.

SP+ certainly hasn't reached many conclusions. In Week 5's ratings below, fewer than two points separate the teams ranked fourth and eighth, and only three separate the teams ranked 10th and 21st. The silliness and unexpected results we've seen to date could continue for a while.

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 will probably fall. If you're strong and unlucky in a loss, it will probably rise.