one of the more reliably stable team stats. Compared to things like running or passing efficiency, the absolute size of penalty rate's effect is small, but because it tends to be consistent, it can be fairly predictive.
This Sunday's conference championship games feature teams on opposite sides of the penalty spectrum. ATL has by far the league's lowest team penalty rate at 0.21 penalty yards per snap. For context, the league average is 0.41, and the next best team is NYG at 0.29. ATL is 3.9 standard deviations better than the 2012 mean! SF is third worst in the league 0.46 penalty yds per snap.
On the other side of things is BAL. They're averaging 0.53 penalty yards per snap, the league's worst rate. That's 1.9 standard deviations worse than the mean. NE is tied for 6th best, at 0.39 penalty yds per snap.
How important a consideration is penalty rate on the outcome of a game? As it stands, the game probability model has the SF-ATL game at 55/45 in favor of SF and the BAL-NE game at 33/67. If I set all four team's penalty rates to the league average and rerun the probabilities, we can directly see how they're affecting the prospects for each team.
The SF-ATL game becomes a 61/39 contest, representing a swing of 6 percentage points. The BAL-NE game becomes a 36/64 match up, representing a smaller swing of 3 percentage points. The swing is larger in the NFC game partially because it begins closer to a 50/50 game, where smaller changes have bigger leverage.
Things are a little less extreme when we look at the actual impact of penalties on each team. The Win Probability Added (WPA) due to penalties for each team this season paints a slightly different picture. WPA is highly senstive to game context, so a 10 yard holding penalty on 1st and 10 from the 50 in the 1st quarter won't have nearly the same effect as the same penalty in the 4th quarter of a tight game. And in a blowout, many penalties would have zero effect on WP.
BAL, with its very high penalty yardage rate, have cost itself 0.50 WPA, (about half a win) in team penalties in the regular season, putting them squarely average in the league at 16th. But BAL benefited from opponent penalties slightly more, to the tune of 0.61 WPA (T 6th), for a net penalty effect of 0.11 WPA (10th).
NE had less of an impact due to own team penalties than BAL, but benefited less from opponent penalties. NE's own penalties cost just 0.19 WPA (best in the league), and benefited by 0.29 WPA (29th), for a net effect of 0.10 WPA (11th), right behind BAL.
SF cost itself 0.36 WPA (8th), which is relatively little considering it's high penalty yardage rate. SF benefited by 0.61 WPA, (T 6th with BAL). All together, that's a net of 0.24 WPA,
ATL, with its amazingly low penalty yardage rate, cost itself 0.36 WPA (7th), and benefited by 0.23 WPA (31st in the league, and not even as much as SF's net WPA). That's a net of -0.13 WPA for ATL, tied for 26th in the league. Tragically, despite playing highly disciplined football all season, ATL has suffered a net negative in terms of penalty effects on wins and losses.
But keep in mind that WPA is not terribly predictive. Teams really can't control other team's proclivities to be penalized. You'd think that might be the case to some degree. Fast WRs can draw pass interference calls, or monster DEs can draw holding penalties. But that doesn't seem to be the case. Opponent penalty stats don't correlate from week to week like own-team penalty stats do.