Philly's Inferno

A sports fan’s opinion through the lens of Philadelphia’s seventh circle of hell.

Month: March, 2013

Like Hunters Stalking Prey, the Eagles Enter Free Agency

PI - Brian-Dawkins2The Philadelphia Eagles entered the new NFL year knowingly.  Under the baking sun, they wandered through the forest and arrived at the pond of free agency.  Some were already there, like the Miami Dolphins, who sprinted forty yards in less than five seconds and dove in, made a huge splash, and held high their large catch.  Braggarts, the Eagles thought.  Others, like the Oakland Raiders and Arizona Cardinals, were already in the pond, treading water and unsure of a direction.  Weaklings.  Then arrived the Philadelphia Eagles, calmly walking around the pond like a hunter stalking prey, observing with interest and smiling slyly, as if to say, “Ha, look at these clowns”.

After their circumnavigation, they paused and turned towards the pond. They did not toe the water.  They did not enter blindly.  They walked into it with purpose, reached into the water and pulled out multi-purpose H-back James Casey.  They reached in again and pulled out DT Isaac Sopoaga.  Then safety Patrick Chung, cornerback Bradley Fletcher, and linebacker Jason Phillips.  From the depths of the free agency pond, they plucked depth for their team.  The Philadelphia Eagles strode from the pond with five players in hand and left the other teams behind.  They will return when they need to, when they want to.  They are executing a plan, decisively, step by step.  And they know there is another, larger pond one month in the distance.

And this is primarily what the first day of free agency has been for the Eagles.  They provided themselves not with big names as they have in the past, prior thinking that they equated to success.  Instead they supplied themselves with depth at positions of need.  They brought in football character and special teams players (huh, who are they?).  None of these players can be characterized as the “one guy” needed to bring a franchise to the next level.  However, collectively they are sure contributors with relatively healthy histories.  Low risk, high reward moves; safe and smart bets. They are the anti-Dream Team.  That is, they are most definitely not pond scum.

Examining the Ratio: Striking a Balance

As Andy Reid settles into his new position in Kansas City and we recover from a pass-heavy hangover (albeit with an unknown offense yet to emerge from the fog ahead), I would love nothing more than to illustrate the importance of running the ball. Unfortunately, my assumption was incorrect.  Running when protecting a lead and passing when playing from behind are phenomena that do not offset each other.  Therefore, the basis for my earlier conclusion that running more often may lead to more Eagles victories is not necessarily true.  But after further research and analysis, it’s not entirely wrong either.

In order to better control for game context and increase statistical significance, I added two more seasons of data (2008 and 2009) and removed all fourth quarter rushing and passing attempts.  I’m making another assumption here (it could be wrong and subject to many exceptions), that most rushing attempts when protecting a lead and most passing attempts when playing from behind occur during the fourth quarter.  The subsequent “adjusted” run/pass and pass/run ratios include only data from the first three quarters of Eagles games during the past five years (80 games).  As expected, these adjustments drastically changed the results of my previous logistic regression, making them less meaningful.  Here is my prior run/pass ratio result along with the new adjusted ratio results:


The odds ratio for the adjusted run/pass ratio indicates that for every one unit increase in the run/pass ratio, the Eagles are over three times more likely to win (a big difference from 38 times more likely to win, as stated earlier).  Compare this with the adjusted pass/run ration, where for every one unit increase, the Eagles are just 44% more likely to win.  It seems that running attempts continue to have a greater impact on game outcomes.  However, these two results have p-values greater than .05, are not statistically significant, and can be ignored.  This pissed me off.

Thanks to feedback from commenters on Philly’s Inferno (mjoedgaard) and Reddit’s /r/eagles and /r/nfl pages (fourth_down_surprise) as well as some great feedback from Bleeding Green Nation and Wingheads, I did more research.  In his 2007 article, Brian Burke from Advanced NFL Stats performed some linear regressions using multiple facets of the game and concluded that passing efficiency correlates more to wins than rushing.  In 2003, Aaron Schatz from Football Outsiders also performed a regression analysis and concluded that teams do not necessarily need to establish the run early to win, and fourth quarter leads dictate more running plays for the winning team (and those running plays are extraordinarily effective).  Burke’s and Schatz’s conclusions seem to agree with my new adjusted logistic regression results (By the way, both of these articles are great. Read them.).  However, they also got me thinking more about balance.  Could balance be important?

Using the same dataset (Eagles games from 2008-2012, first through third quarter only), I created a statistic, “Attempts from Balance”, which is the number of attempts (rushing or passing) needed to achieve a one-to-one run/pass ratio.  I wanted to test the hypothesis that, as the attempts from balance decrease (or the closer to a balanced attack the team gets), the more likely the team can win.  Here is the result:


The result of the logistic regression is statistically significant (p-value < .05) and indicates that for every one unit decrease in attempts from balance during the first three quarters (where one unit represents five attempts), the Eagles were nearly 2.5 times more likely to win.  Here is a breakdown of the probabilities:


During games in which the Eagles executed a perfectly balanced attack through three quarters, they had a 78% chance of winning.  When the team had between six and ten more rushing attempts than passing attempts, or passing attempts than rushing attempts, their win probability dropped to 37%.  (Not included in the table are two games in which the Eagles had more than 12 passing attempts from balance.  Disagreeing with this statistical model, the Eagles won both games.)  This seems to illustrate that yes, balance is important and correlates with wins.

Of course, there are still many unforeseen variables at play here, and the direction of this correlation cannot be assumed.  We can very easily say that game situations during the first three quarters over an 80-game span dictate balance, rather than balance dictating the result (although I think as the dataset grows, this becomes less likely). Also, this does not, on the surface, seem to agree with Burke’s and Schatz’s conclusions that passing is more important.  However, their work is a result of linear regressions in which season stats are compared to aggregate numbers of wins, rather than non-linear regressions comparing single game stats and outcomes.  But it’s hard to dismiss (and rather fun to accept) that this analysis does seem to jive with nearly every Eagle fan’s frustration during Andy Reid’s pass-first-answer-questions-later tenure.  So maybe Chip Kelly should take note: strike with a balanced attack and pound the damn ball with ferocity.

Click here for the detailed logistic regression file: Eagles Run Ratio – Logistic Regression

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Examining the Ratio: The Importance of Running the Ball for the Philadelphia Eagles

Eagles Defensive Coordinator Billy Davis’ father, Bill Davis, served as the Eagles’ linebackers coach under Dick Vermeil and also coached the special teams in 1977 and 1978. After Bill transitioned to Cleveland, first as Director, then as Vice President of Player Personnel, he returned to Philadelphia in 1988 when Eagles President Harry Gamble hired him to be the team’s Vice President of Player Personnel. Bill was charged with helping head coach Buddy Ryan evaluate and bring in more talented players. When Bill Davis resigned after the 1989 season, Buddy offered the position to Ted Plumb, his offensive coordinator for four years (Plumb didn’t take it). Along with the fans, Buddy had grown tired of Plumb’s ineffective play calling and wanted to move in a more exciting direction (unfortunately, that direction was Rich Kotite). Under Plumb, the Eagles offense had become predictable. Series after maddening series, Plumb routinely called runs on first down, runs on second, and passes on third. It’s interesting then, to contrast that era with the fatigue surrounding Andy Reid’s pass-first philosophy. As Chip Kelly and Harry Gamble’s son, Tom, continue to weigh pros and cons for potential starting quarterbacks, a lot of emphasis has been placed recently on the Eagles passing game. But perhaps this should be an echo of the past and not represent what may be most important. Instead, it might be beneficial to re-examine, or quantify, how significant running the ball is for this football team.

Since the NFL is so clearly cyclical, both in playing trends (and now, evidently, with coaching and front office legacies), how important is a balanced attack for today’s Philadelphia Eagles? In the last three years, Andy Reid’s teams have had a pass/run ratio of 1.3 to 1. In the team’s 22 wins, that ratio dropped to 1.1 to 1, and in the team’s 26 losses the ratio increased 1.6 to 1. This seems to indicate that yes, a more balanced attack leads to more wins. However, in seven of those 26 losses, the Eagles had a balanced attack (a ratio of 1.3 to 1 or below), and in eight of the team’s 22 wins, they did not (a ratio greater than 1.3 to 1). This indicates that averages don’t tell the whole story. If we wish to examine whether a lower pass/run ratio, or rather, a higher run/pass ratio, truly results in more wins, we can perform a logistic regression.

Logistic regression can be used when we want to see the strength and significance between some independent variable and a dependent, dichotomous outcome. In other words, we want to see how the run/pass ratio for each Eagles game in the past three years related to wins and losses. If results are statistically significant, the logistic regression model will produce a p-value less than .001. If results are strong, a statistic called an odds ratio, which in this case will represent the ratio of winning odds to losing odds, will be high. After entering the run/pass ratios and win/loss data from the last three years into a logistic regression function, here are the primary results (detail here – Eagles Run Ratio – Logistic Regression):



Since the p-value is less than .001, the results are statistically significant. This is substantial because it means the high odds ratio (38.1306) is meaningful. In effect, the results of the logistic regression model tell us that there is indeed a strong, significant relationship between the run/pass ratio and wins and losses. As the run/pass ratio increases, or the more often the Eagles run the ball, the more likely they are to win a football game. In fact, every time the run/pass ratio increases by one unit, the Eagles are 38 times more likely to win a football game. For example, on October 9, 2011 in Buffalo, the Eagles rushed 20 times and passed 40, resulting in a .50 run/pass ratio. According to this logistic regression model, that ratio gives the Eagles a 22.44% chance of winning (they lost 31-24). But on December 18, 2011 against the New York Jets, the Eagles rushed 33 times and passed 22, a 1.5 run/pass ratio and a one unit increase over the .50 ratio from the Buffalo game. In this model, a 1.5 run/pass ratio gives the Eagles a 91.7% chance of winning (they beat New York 45-19), and means that the Eagles were 38 times more likely to win with that higher run/pass ratio against New York than with the run/pass ratio against Buffalo (click on the file above for win probabilities for each of the Eagles 48 games).

In an NFL where passing and quarterback play are held in higher regard, these results are counter-intuitive. They indicate that, for our Eagles, running the ball more often will result in more victories. But these results must be taken with a grain of salt. The regression does not control for increased rushing attempts when protecting a lead, or increased passing attempts when playing from behind. However, these phenomena may offset each other. Also, this is a historical analysis with a relatively small sample size. And since Andy Reid is no longer the head coach, these results may not project to Chip Kelly’s team. But the NFL is also cyclical. For example, if history is any indication, the 2013 Billy Davis/Tom Gamble tandem will bode well (During Bill Davis and Harry Gamble’s first year together, the Eagles drafted Keith Jackson and Eric Allen). It’s also exciting to consider that, for a head coach with a fondness for science, these results may foretell the next trend in Eagles football. And it just so happens we have one of the best running backs in the league currently on the roster.

*Updated 3/2/2013 to include comment regarding game context.

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