## Defense Penalties Puzzle Solved

In an earlier post, I found that penalties committed by a team's defense correlated postively with team wins. In other words, the more penalties committed on defense, the more games a team could expect to win. I was confused by this result and re-checked my math several times, but it always came out the same.

I finally realized the cause of the result. What the stat services call defensive penalties are actually penalties committed by opposing teams on offense and defense. And what they call offensive penalties are penalties committed by one's own team on offense and defense. All the stat sites that I've used for data use the same nomenclature: nfl.com, sportsline.com, and espn.com. I don't know why it's done like that.

It seems all the big websites use data from Stats, Inc., so I bet that's how they do it there. Unfortunately, NFL gamebooks, the official box scores of NFL games, do not breakout a team's penalties between offense and defense.

As an explanatory variable, it's valid--opposition penalties help explain what makes teams win. But as a predictive variable for season wins, it's useless and should be removed. This means some revisions are in order for my models. The good news is that it doesn't change the models' predictions in a significant way because the solution is to remove the variable. And fortunately, a team's opposition's penalty stats tends to average out throughout the season, so removing a variable that is very average doesn't effect the dependent variable (team wins) appreciably.

### 9 Responses to “Defense Penalties Puzzle Solved”

1. Anonymous says:

Brian,
Thanks for all the work you've done with this site. I look forward to visiting it daily.

I've been using the Fox Sports stats for my system and they have the penalties by offense and defense listed.

Go here to find the penalty stats.
http://msn.foxsports.com/nfl/sortableStatsTeam?div=NFL&stype=defense&stable=downs&stat=penTot&dir=ascending&season=regular

You can copy and paste it to your address bar if the link isn't clickable.

2. Brian Burke says:

Thank you very much, but unfortunately the Fox site also names penalties the same way.

Offensive penalties are those committed by one's own team, and defensive penalties are committed by the team's opponents. There is no actaul differentiation between penalties committed by an offense or defense.

I verified this by looking at 2006 post-season stats on the sites in question. I looked at teams that only played one playoff game. For example, the Ravens played a single game against the Colts. In that game the official NFL gamebook says the Ravens, as a whole, committed 6 penalties for 39 yds and the Colts committed 3 for 19 yds. The stat sites all list the Ravens has having committed 6 "offensive" penalties for 39 yds and 3 "defensive" penalties for 19 yds.

The big clue was that over the past 5 seasons, the total number of offensive and defensive penalties and penalty yards were exactly equal. The only realistic explanation was that they were actually penalties for and against, not offense and defense.

Notice at the bottom of the Fox web page they site the stats are from Stats, Inc. Also, the ESPN site and the Fox site are practically identical, as are the Sportsline and NFL sites.

3. Derek says:

When I was naming the variables, I decided to label penalties as either given or received.

4. Brian Burke says:

Derek-I'm glad you knew about this already, but do you see my point about predicitive capability?

The penalties that opposing teams committed in previous games has no predictive value in future games.

They can help explain why teams won retrospectively, however.

5. Derek says:

Have you read the St. Louis Rams chapter of Pro Football Prospectus 2007 yet? I was just leafing through it, and it turns out they have a section about penalties and their correlations with losses. It turns out that actual defensive penalties, not the ones Stats Inc list, have a <0.1 correlation with losing. The reason they give: "Defensive penalties are often a byproduct of good defensive play." Offensive penalties (except maybe holding) are simply mistakes.

6. Brian Burke says:

Interesting. Coincidentally, I just got back from the book store looking for PFP. They didn't have it yet.

I read somewhere it has YAC listed by QB, which could complete my effort for a valid passer rating.

7. Anonymous says:

Brian,
Do you happen to know what the most frequently called penalty in the NFL is? I stumbled across your site while looking for this information and it seems like that might be something you'd know. Thanks!
Dave

8. Chuck says:

i am curious about any trends in pass interference the last 10 years or so.

9. Unknown says:

I was looking for a site with some data to validate a penalty tracker I was making and stumbled across this. I realize this is older than dirt, but I will shortly be adding the offensive/defensive breakdown. (Maybe this weekend.) Keep an eye out for it if you're still needing that.

http://nfl-penalties.nutcan.com/

Right now it just has the penalties against/penalties for breakdown which as you noted are commonly confusingly labeled offensive and defensive penalties.

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