Now that the College Football season is behind us and the Clemson Tigers have claimed the National Title, I decided to look back at the final stats and see how defensive PPG impacted wins during the 2018 season. With all the hype surrounding Offense in both college & professional football this season, I wanted to make sure that the truth about football is still being told. That truth being that Defense Points Per Game still remains a stronger predictor of wins than scoring PPG.
Huh , what ? Did he really just say that? Yup, I did. Although both Points Per Game & Defensive Points Per Game individually both have a an effect on Wins, its Defensive Points Per Game that has a stronger predictive strength in terms of its effect on Wins. This is not the narrative that you will see on TV or hear on the radio but its the truth! See for yourself.
Defensive Points Per Game
By using a regression analysis, we can see how both points points per game & defensive points per game impact wins. A Regression analysis is a powerful statistical method that allows you to examine the relationship between two or more variables of interest. It is a way of mathematically sorting out which of those variables does indeed have an impact.
The (Predictive Strength) tells us the proportion of the variance in the dependent variable that is predictable from the independent variable. A PS of 100% would indicate that the model explains all the variability of the response data around its mean. You can see from the chart above that 53% of the variability of Wins is explained by Defensive Points Per Game, while 49% of the variability of Wins is explained by Points Per Game.
The graph above shows you the linear relationship between wins and defensive points per game. Simply put as the defensive points per game increase, the average number of wins decrease.
The graph below puts all 130 FBS into 5 groups of Defensive Points Per Game along with their average number of wins for the that group. You can see that the group with less than 21.8 Def PPG averaged 9.7 wins while the group between 25.5 - 28.70 had an average of 6.4 Wins among them.
Conclusion
Independently, both Defensive PPG & Points PPG have a strong main effect on wins but neither is a perfect predictor. Predictions and Forecasts are all about likelyhood and probability. There are always outliers such as Mississippi State who held opponents to 13.2 points per game and went 8-5, while Oklahoma gives up 33.3 ppg and wins 12 games. Remember the predictive strength on wins is 53% so that while Def PPG has a significant and strong main effect on wins, its not a perfect predictor.
Fact is, that according to 2018 data, Defensive PPG has a stronger predictive strength than Offensive PPG in terms of its effect on wins. However this is not the narrative that we are led to believe. You hear about hi scoring & hi flying offense & Kyler Murray and Oklahoma making the playoff. The media declares that the mantra of "Defense wins Championships" is dead. Sure thats a sexier narrative and probally gains more viewers or listeners, but its simply not true. You have to resist the notion from many of the talking heads on sports TV & radio that defense no longer matters and focus on the statistics.
As a coach, one of the quickest ways to improve your team is by improving on defense. Maybe your team isn't in the college football playoff but as you can see from the charts above, the difference between 8 wins or 5 wins can be just 3-4 points per game on defense. These are numbers you can share with your players to motivate them and show them just how close they are to a bowl game or 9-10 win season!
Next time , I will show you how the combination of Offensive PPG & Defensive PPG is really what matters but in the mean time you can check out the complete list of Def PPG leaders along with their win totals. As always, feel free to reach out to me anytime with questions or requests info@acefootballanalytics.com or join our mailing list through the link.
DEFENSE PPG LEADERS & Wins (All Games except CFB National Championship)
