Game Probabilities - Week 14

Weekly game probabilities are available now at the nytimes.com Fifth Down. This week I also lead-in with a discussion of the luckiest and unluckiest teams so far this season.

Luckiest and Unluckiest Teams - Week 14

For some reason this is my favorite stat.

I estimate team "luck" by using my efficiency regression model to calculate each team's expected wins--how many wins a team can normally expect, on average, given their actual performance in offensive and defensive running, passing, turnovers, and penalties. The difference between the expected wins and actual wins is what I loosely call team luck.


What do I mean by luck?

In my own life, I'm a big believer in hard work, preparation, focus, execution and everything else that isn't luck. Coaches and players can't let themselves think any other way for a single second. But once we account for all those things, what do we call what's left over? Statisticians call it "residual," and a substantial portion of any residual is due to random effect, including sample error and what I call "bunching." In a bounded and meticulously measured system like sports, a vast amount of the residual from any decent model will be due to randomness. A season of 16 games simply isn't long enough for the breaks to even out.

Team Efficiency Rankings - Week 14

The team rankings below are in terms of generic win probability. The GWP is the probability a team would beat the league average team at a neutral site. Each team's opponent's average GWP is also listed, which can be considered to-date strength of schedule, and all ratings include adjustments for opponent strength.

Offensive rank (ORANK) is offensive generic win probability, which is based on each team's offensive efficiency stats only. In other words, it's the team's GWP assuming it had a league-average defense. DRANK is is a team's generic win probability rank assuming it had a league-average offense.

GWP is based on a logistic regression model applied to current team stats. The model includes offensive and defensive passing and running efficiency, offensive turnover rates, defensive interception rates, and team penalty rates. If you're scratching your head wondering why a team is ranked where it is, just scroll down to the second table to see the stats of all 32 teams.

Games of the Week

Game of the Week: OAK 27 at PIT 24 (6.7 Excitement Index)
Runner Up: NE 21 at MIA 22 (6.2 EI)

Comeback of the week: NO 33 at WAS 30 (100 Comeback Factor)

Defensive Run-Pass Balance

I've been writing a lot about offensive run-pass balance lately, recommending that most teams should pass more often. So far I've ignored half of the equation--Defensive strategies matter too.

Unlike offensive play choices which are discrete defined options (such as either run or pass), defenses have a continuum of options ranging from a prevent defense to a goal-line stand. Defenses don't have to commit to one or the other. Instead, they can bias their strategy anywhere from 100% pass to 100% run.

With play-by-play data, we know what option an offense chose. Unfortunately, without coach's film of every game and an intimate knowledge of a teams' defensive schemes and intentions, it's nearly impossible to know where on the continuum a defense stood on any given play.

Still, it may be useful to see how often a team was run against or passed against, and see how successful each play type was. The table below lists each defense's proportion of passes faced on first downs. Also listed is the average success of each type of play as measured by Expected Points Added (EPA). The difference in average success between passes-against and runs-against roughly measures the imbalance in play selection.

MVP Candidates Through the Lens of WPA

One of the cool things to do with a Win Probability model is to look at the total Win Probability Added (WPA) of a player. Each play in a game changes a team's chances of winning either positively or negatively, and the WPA for the plays in which a player takes part can be tallied. WPA discounts 'trash-time' performance, and emphasizes 'clutch' performance. The result roughly measures the past value of a player in terms of what matters most--winning games.

WPA is a narrative statistic. It tells the story of how a player performed, but it does not predict how he'll likely play in the future. It includes all the flukes, miracles, and everything else that makes football unpredictable and fun to watch. In essence, WPA is what the MVP award is all about.

I've tallied the WPA for the notable MVP candidates through Week 12 of the 2009 season. The table below lists various players and their WPA expressed a few different ways. There is total WPA, which is simply a raw sum. There is also WPA per game and WPA per play, which tell a slightly different story.

2009 Team-Specific Run-Pass Balance

Recently I've been looking at run-pass balance on first downs based on a principle of game theory. When strategy mixes are optimized, the two strategies will ideally produce equal payoffs. If they aren't equal, then the better strategy should be selected until the opponent responds with his own counter-strategy. Results suggested that, in the NFL overall, the gains by passing on first down exceed those by running. In turn, this suggests that offenses should pass more often than they currently do.

However, every team has its own relative ability between passing and running. You can't just tell the 2009 Raiders to start passing more often. Their running game may actually be superior to their passing game in terms of expected payoffs, so while most teams should be passing more frequently, it's possible a minority of teams should be running more often.

Team Playoff Probabilities - Week 13

Courtesy of NFL-Forecast.com, here are the latest playoff forecasts. The tables below do not include results from the Thursday games.

It looks like the AFC wildcard picture has changed with the Jaguars' and Texans' losses, and the Ravens' win over the Steelers. Although the Ravens currently hold the 6th seed (I think), they're projected to have a 40% chance of holding on to it.

The NFC wildcard picture has changed too. The Packers' and 49ers' chances have improved while the Giants' and Falcons' chances have taken a hit.