Chip Kelly: Success Formula and Offensive Efficiency

Eagles Head Coach Chip Kelly finds his offensive success in certain areas.The doctor is in. That much is certain after Dr. Chip Kelly and co-surgeons Dr. Tom Gamble and Dr. Howie Roseman removed NFL players from the free agency pool with surgical precision. They have resuscitated a team whose health was failing and now they must oversee the rehabilitation. First up, the offense. Dr. Kelly, winner of the Nobel Prize for NFL Innovation for his contributions to Super Bowl winning franchises, measures offensive success with a mathematical formula. But does the formula represent philosophy, or fact? Well, the fact that the formula measures offensive success may be a misnomer. Success may be better measured by yards or touchdowns. More accurately it is a formula for offensive efficiency. Kelly’s formula is defined as follows:

(Total Plays – Dropped Balls – Offensive Penalties – Additional Plays for Negative Yardage)

Total Plays

According to his theory, when Kelly’s teams meet or exceed the 80% “efficiency” mark in any particular game, they win. However, such efficiency could merely be a byproduct of the college game, and not represent current NFL realities. Regardless, we can apply this formula and the 80% threshold to the last five Eagle’s seasons in order to see how well it translates to the NFL. To do this, I modified Kelly’s formula to accommodate my dataset:

(Rushing Attempts + Pass Completions)

(Rushing Attempts + Pass Attempts + Offensive Penalties)

I believe the modifications keep with the spirit of Kelly’s intent, if not the letter of it. For example, dropped balls and interceptions are assumed within the new formula, however, I do not account for negative rushing plays (including fumbles lost), so this could inflate the percentages slightly (we could also argue that by excluding fumbles, we’re controlling for unknown external variables). Regardless, the results are interesting. The Eagles least efficient game in the last five years (56.25%) came on October 18, 2009 in a 13-9 loss to the then 1-4 Oakland Raiders. Donovan McNabb was 22 for 46 with 269 yards passing, no interceptions, but was sacked six times. Brian Westbrook and LeSean McCoy combined for only eleven carries for 63 yards and the offense was penalized four times. The Eagles most efficient game, on the other hand, was the 2008 season opener against St. Louis. They defeated the Rams 38-3 while posting an 87.57% efficiency rate. McNabb was 21 for 33 for 361 yards and three touchdowns. They also rushed 32 times for 108 yards and two touchdowns, and the team committed two offensive penalties. In the Eagles’ last 80 regular season games, they have met or exceeded the 80% threshold eighteen times. Of those eighteen games, the Eagles won fifteen of them, or 83.33%. When they did not exceed the 80% threshold (62 games), the Eagles won 43.5% of the time. So while not an absolute, there rings some truth to Kelly’s theory – the Eagles indeed won more games in which they met or exceeded 80% efficiency. And according to logistic regression models, the Eagles are nearly 6 ½ times more likely to win when meeting or exceeding the 80% mark, and more than five times more likely to win for every ten percentage point-increase in efficiency (say, from 70% to 80%). Here are the win probabilities for select efficiency rates:

HP3

When the Eagles are less than 65% efficient on offense, they have a less than 25% chance of winning. However, when they exceed 80% efficiency, they have better than a 77% chance of winning. So then, Dr. Kelly’s formula for success appears to not only apply to college, but evidence suggests his theory may work in the NFL as well. After all, “football is football”. But it is up to Kelly and his team of surgeons to provide the Eagles with the necessary tools for rehabilitation, tools that help maximize efficiency. The recent signing of multi-purpose H-back James Casey is a great example. It is encouraging then, to see that Kelly and his team appear to want to cure what ails the Eagles by transplantation, rather than treat the team symptomatically.

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Jerome's Friend

Jerome's Friend is a native Philadelphian raised properly by great parents who taught him to love the Eagles and abhor the Cowboys. A new parent himself, he hopes to instill those same fundamental values in his son, who at five months-old can already spike a football. If you follow him on Twitter (@JeromesFriend), you'll also find his Eagles and Philadelphia sports blog, Philly's Inferno, where he resides as a Friend of Jerome.


One Response

  1. [...] The doctor is in. That much is certain after Dr. Chip Kelly and co-surgeons Dr. Tom Gamble and Dr. Howie Roseman removed NFL players from the free agency pool with surgical precision. They have resuscitated a team whose health was failing and now they must oversee the rehabilitation. First up, the offense. Dr. Kelly, winner of the Nobel Prize for NFL Innovation for his contributions to Super Bowl winning franchises, measures offensive success with a mathematical formula. But does the formula represent philosophy, or fact? Well, the fact that the formula measures offensive success may be a misnomer. Success may be better measured by yards or touchdowns. More accurately it is a formula for offensive efficiency.  Read more…  [...]