Closing In On NFL Defensive Evaluation Tool


I have finally found something mathematically significant in my now week long study of NFL defenses. It’s not what I was hoping for, but ultimately it might be the best measure for the quality of a defense that we have. I’m going to continue to work with the data to develop a statistical model that fits all the data that I’ve presented over the last week, but I’m now very close to the ultimate defensive analysis tool I was after.

First a recap:

The NFL uses yard allowed to rate defense. We all know this is extremely flawed. Yards allowed doesn’t correlate highly to points allowed, and thus it doesn’t correlate to wins. It’s just a poor measure. I also showed that yards allowed was highly dependent on the # of possessions, which is something the defense has no control over.

The other measurement current used is points allowed. This is especially true for fans of teams like Seattle; a team that was #1 in that category, despite being less than steller in other statical measures. The problem is that this is also dependent on the number of possessions, and I also have shown that it is dependent on the average starting field position for the opponents. Again, these are things that the defense can’t control.

This problem led me to break down the results of each drive by it’s conclusion: touchdowns, punts, etc. The result there was too many variables and nothing to regress that data to. While there was plenty of anecdotal results that were very interesting, there wasn’t anything significant mathematically that could be found at this point.

Recap over. Now on to new results.

This time,  looked at something simple: yards per drive. It’s is one of the only factors that the defense has full control over. The better the defense, the quicker they’ll get off the field, right? Sure, there’s the “bend but don’t break” philosophy  but while that might be functional, it’s is hardly dominant.

The problem here is that this evaluation of the defensive play doesn’t correlate highly to anything significant, like points given up, or wins. There’s just too many other factors that effect those things we’d want to correlate it to.

To begin to account for that, I took the average starting field position for each defense, and added that to the yards given up to give me the average yard yard where drives ended.

That number, actually correlated quite nicely to points given up. It’s still not perfect, and there’s still one more variable I need to account for (getting turnovers appears to be a big factor), but I think that I may have stumbled on to something that is very mathematically significant.

Unfortunately, it’s very late here, so that’s going to have to wait until tomorrow. I will say that once I account for turnovers, i believe I’ll end up showing that yards per drive is an extremely accurate indicator of how well a defense played.

Until then, I’ll just leave you with today’s data:

RkTeamyards/drRkTeamave drive end1Denver Broncos25.011Denver Broncos49.242Pittsburgh Steelers25.362San Francisco 49ers47.873Chicago Bears26.303Chicago Bears47.754Arizona Cardinals26.374Cincinnati Bengals47.045Houston Texans26.395Arizona Cardinals45.976San Francisco 49ers27.236Seattle Seahawks45.937Cincinnati Bengals27.507Houston Texans45.638New York Jets27.678Pittsburgh Steelers44.779Green Bay Packers29.289Green Bay Packers44.7610Detroit Lions29.5010San Diego Chargers44.1911Baltimore Ravens29.5511New York Jets43.9412San Diego Chargers29.6812Baltimore Ravens43.4313Seattle Seahawks29.8713New England Patriots43.1314Cleveland Browns30.0114Cleveland Browns42.8515Minnesota Vikings30.9415Minnesota Vikings41.8016St. Louis Rams31.1516Atlanta Falcons41.6717Philadelphia Eagles31.2017Tampa Bay Buccaneers41.0818New England Patriots31.2718Detroit Lions40.9119Carolina Panthers31.3519Indianapolis Colts40.4120Oakland Raiders31.5120Miami Dolphins40.2321Miami Dolphins32.0721Carolina Panthers40.0022Buffalo Bills32.4422Dallas Cowboys39.9423Tampa Bay Buccaneers32.5023St. Louis Rams39.2624Tennessee Titans32.6024Jacksonville Jaguars39.1825Kansas City Chiefs32.9725Kansas City Chiefs39.0526Atlanta Falcons33.2326Washington Redskins38.2327Jacksonville Jaguars33.2727Oakland Raiders37.6228Dallas Cowboys33.8528Tennessee Titans37.3629Washington Redskins34.1429Buffalo Bills37.3530Indianapolis Colts34.6130Philadelphia Eagles36.9431New York Giants36.0831New York Giants36.0832New Orleans Saints37.6632New Orleans Saints33.02