Part of the discussions regarding the "ranking" of the Eagles defense was that this defense was only ranked so high because it beat up on "bad" teams. As we've seen ad nauseam now, the Eagles defense ended the year ranked 10th in PPG and 8th in YPG. I've decided to do a fairly simple analysis to determine how much this defense was beating up on the bad teams. Since this is a team sport, I also looked at the Eagles offense because they were highly ranked as well, 8th in PPG and 4th in YPG to be exact.
After the jump is an explanation of my methodology, some charts and quick thoughts about each of them.
To conduct this I came up with an "adjusted" PPG for all of the NFL offenses and defenses. Don't worry, it's fairly simple and not all Football Outsidery.
The rankings for both offense and defense are based upon the TOTAL team points scored and TOTAL team points given up. These include special teams and defensive touchdowns. Obviously, it's not the defense's fault if the offense throws a pick six and the offenses shouldn't get credit if their defense scores a pick six. So I adjusted all of the NFL teams' points for and against by taking out those special team/defensive TD's plus their subsequent extra points. For example, the Eagles scored 396 points on the year for an average of 24.8 PPG. But, the defense (we had no special team TDs) scored of 30 of those points (4 TDs and a safety). In reality the offense was only responsible for 366 points, or 22.9 PPG. And for the Eagles defense, there was 14 points scored against the Eagles when the defense wasn't even on the field. That drops their total points and average from 328 and 20.5 to 314 and 19.6.
I adjusted all of the points for and against for all the teams and then re-ranked them. The Eagles offense and defense each fell by a spot in the rankings to 9 and 11 respectively.
Ok, so all of that was to explain where my rankings and averages came from. On to the charts. For these charts I took the difference between the points scored by just the Eagles' offense or given up by just the Eagle's defense and their opponent's adjusted season averages given up and scored. I then plotted those differences against their adjusted rankings in order from lowest to highest. The lower the ranking, the better the defense/offense the Eagles were playing against. That means that if the Eagles were beating up on bad teams for both offense and defense, then the results to the far right would be much better.
First up is the Eagles offensive performance. The blue bars are wins and the red bars are losses. The gray bars are the differentials between the opponent's offense and defense. That means that if the defense held the opponent to its offense's average that's how much the Eagles would have to outscore their opponent by in order to win. For offense, having a positive differential is better. That means the Eagles outscored their opponent's defensive season average.
My takeaways from this chart:
• Eagles didn't really beat up on the bad teams any more than the rest of the league. In fact they were on the positive side against 5 of the best 8 defenses they faced this year.
• Twice the Eagles lost despite outscoring the opponent's defense by 9+ pts. Just looking at the numbers I would say the offense did its job those two games and the defense cost the Eagles those games.
• In one game, the offense failed to make up the differential yet the Eagles still won. Just based upon the numbers, I would say the Eagles defense stole that game for them.
Next is the Eagles defensive performance. For this chart, negative is better. That means the Eagles held their opponent to less than their season average. The gray bars are the difference between the opponent's defensive and offensive averages. That is the number of points that the defense would have to hold the opponent's offense to if the Eagles' offense only scored the number of points that their opponent's gave up on average.
• Similar to the offense, the Eagles really didn't beat up on the bad teams. In fact they did pretty well against some of the better offenses they played.
• Except for the Ram's game, the Eagles only won when the defense held their opponent to less than their opponent's season average, but the defense was still below the differential so it shouldn't have mattered anyways.
• There was one game where the defense held their opponent below their opponent's team differential, but the Eagles still lost. I would put that game on the offense.
I also plotted the differentials between the yards gained and given up and the opponent's season averages. I consider this another way to see how much each unit was beating up on the bad teams. As with the other charts, the blue bars are wins and the red bars are losses. Positive is good for offense and bad for defense.
Both units did a good job of gaining more or giving up less against the better teams the Eagles faced.
Here is a table of some of the raw data.
What are your thoughts on the charts I presented?
If you have any questions about this work put them in the comments and I will do my best to answer them. Also, if there are any other relationships or data you would like to see that pertains to what I've presented here let me know and I will see if I have time to oblige.
Random Stats I came across while doing this:
• Biggest difference between Standard Offensive Ranking and Adjusted was the Bears. They went from 17th to 24th. They had 72 points from their defense and special teams.
• The Saints had the highest Adj PPG for the season at 32.4. The Packers were 31.9.
• The Rams were a paltry 10.9 Adj PPG.
• Biggest difference between Standard Defensive Ranking and Adjusted were the Chiefs (12th to 17th), the Falcons (18th to 13th) and Jets (20th to 15th).
• Jets had the most defensive/special teams points scored against them with 44.
Update: I forgot to give credit where credit is due. I used http://www.pro-football-reference.com/ as the starting source for all of my data.