What is SP+? In a single sentence, it’s a tempo- and opponent-adjusted measure of college football efficiency.
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.
espn.com article