Cowboys vs. Chargers Trends
At ABC, I posted a statistical preview of the Cowboys vs. Chargers game. Here’s the intro:
To stat geeks like me, there are three little letters that represent the most explanatory, most predictive, and most fascinating stat in all of sports: EPA. The Environmental Protection Agency might have a stronghold on the acronym among the general public, but in the world of sports analytics, EPA is all about expected points added.
With most of the stats I discuss, the aim is typically to uncover how closely perception matches reality—how easily things could have gone differently. I want to find out how a team will perform in the future, emphasizing the process of how they’re doing things instead of the results.
In terms of future points, past points is only a moderately good predictor. Let’s face it: points are relatively fluky. We see offenses score because their defense give them the ball in opponent territory or fail to score after driving 80 yards all the time. So we want to know how well offenses (and defenses) are really performing, and how many points they should be scoring relative to their performance.
EPA captures that. Using historic game data, sites like Advanced NFL Stats can very accurately predict the number of points a team can be expected to score on any given drive. A first-and-10 at your own 20-yard line has historically been worth a net of +0.34 points to an offense, i.e. they could be expected to outscore the opponent by 0.34 points, given that particular game situation. An average offense in such a situation would have a 15 percent chance of scoring a touchdown and an eight percent chance of connecting on a field goal.
So if we know the point expectation before a play and we know it after a play, we can measure the difference to see how well a team is playing. That’s EPA.
The Cowboys currently rank fifth in the NFL in points with 83. That’s awesome, but it doesn’t tell us much about the Cowboys’ offense because the play of a team’s offense, defense, and special teams are so connected. They’re tied together in such a way that we could never separate them studying points scored or allowed. For years, Dallas has ranked really high in yards but really low in points because their defense failed to put them in advantageous situations. Points scored is just a really poor barometer for offensive strength.