Four top-10 teams -- and nine ranked teams in all -- lost in Week 5 of the 2021 college football season, and the wackiness and chaos levels are higher than they've been in years. As you would expect, Week 5's unpredictability has resulted in a lot of movement in the SP+ ratings. However, the top three remain the same: Georgia, Alabama, and a rapidly improving Ohio State lead the way, a few steps ahead of everyone else.
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.