Deflategate and Fumbling Rates

By John Acton

Some of the most controversial analysis of Deflategate has focused on the Patriots’ fumble rate since 2007 (the year that the current rules about football handling were implemented, after Tom Brady circulated a letter to other quarterbacks to petition the NFL to make the change). In particular, Warren Sharp has put forward the notion that the Patriots’ fumble rate has been suspiciously low, and that the players who had previously played for the Patriots had significantly higher fumble rates than they had when in a Patriots’ uniform. Sharp’s methodology has been criticized by a variety of sources for using both bad data and a statistically problematic methodology. That being said, the gist of the question Sharp is asking has validity. If the same players fumble less for the post-2007 Patriots than for other teams (or for the pre-2007 Patriots), it would raise questions about whether the Patriots were doing something that made fumbling less likely.

There are 10 players who had at least one rushing attempt or reception for the Patriots both before and after 2007, 45 players who had at least one rushing attempt or reception for the post-2007 Patriots and at least one other team, and 8 players who fall in both categories. I compiled the data for the number of combined rushing attempts and receptions (from here on called “touches”) for all of these players, categorizing them into touches with the pre-2007 Patriots, touches with the post-2007 Patriots, and touches with other teams.

Unfortunately, it is very difficult to get any statistically significant results based on this information, because fumbles are very rare among both good and bad players. As such, it takes a very large sample size for good and bad fumble rates to distinguish themselves at a 95% confidence interval. That being said, when comparing the 3 categories between these different players, the following statistically significant results are found:

  • Kevin Faulk had a lower fumble rate post-2007 than pre-2007. (0/433 vs. 16/1001 p-value: 0.00804)
  • Benjarvus Green-Ellis had a lower fumble rate with the post-2007 Patriots than with the Bengals. (0/588 vs. 5/545 p-value: 0.0198)
  • Benjamin Watson had a lower fumble rate with the Browns and Saints than with the pre-2007 Patriots. (1/196 vs. 5/95 p-value: 0.00736)

This doesn’t show us very much. It’s worth noting that Faulk and Green-Ellis are the only two players to record more than 400 touches in more than one category, and both of them show up as statistically significant, going eye-raising amounts of time without a single fumble for the post-2007 Patriots. There are also some very suspicious-looking rates that still miss statistical significance, such as Tom Brady (9/262 vs. 17/277), Matt Cassel (3/77 vs. 17/166), and Danny Amendola (0/92 vs. 4/208). On the other hand, Benjamin Watson’s significant improvement with the Browns and Saints gives precedent for an individual’s fumble rate drastically changing over time for reasons that have nothing to do with the inflation of the ball.

However, in the aggregate, there is significantly more information to believe that the post-2007 Patriots are fundamentally different. The 10 players who played for the Patriots both before and after 2007 had 42 fumbles on 2,023 touches pre-2007. After 2007, these same 10 players had their fumble rate nearly cut in half, fumbling only 18 times on 1,729 touches. This drop has a p-value of 0.01174, and suggests that something changed to drastically cut these 10 players’ fumble rates.

The aggregate difference between players who played for the post-2007 Patriots and their performance with other teams is less pronounced, but still statistically significant. After 2007, these 45 players combined for 32 fumbles on 4,506 touches in a Patriots uniform. With other teams, these same players combined for 154 fumbles on 13,340 touches for a p-value of 0.01108.

There may not be enough data to clearly prove that the Patriots fumble rate is substantially different from the rest of the NFL’s, and it’s always possible that the Patriots changed some variable in their play-calling or personnel decisions around 2007 that created this positive impact. But the data clearly shows that in general, post-2007 Patriots players were not able to replicate their lack of fumbling in any other time or place in their career. This may not exonerate Sharp’s methods, but it does help his point: the data raises serious questions about whether or not the Patriots fumble rate has been kept artificially low.

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  • It’s called coaching. If you fumble on BB’s team, you don’t play. The answer to the “serious question” you raise at the end is that the Patriots’ fumble rate is indeed “artificially” low, if you include the artifice of coaching. They simply take better care of the ball. That’s not that hard to figure out.

    The /only/ interesting metric here would be pre-2007 PATRIOTS vs post-2007 PATRIOTS, which, as you say yourself “doesn’t show us very much” for lack of sample size. I don’t get how a player’s behavior on other teams could in any way be relevantly measurable. There are so many just regular old anecdotal cases of players who thrive in one environment and bomb in another, and that has nothing to do with the patriots.

  • Have you considered a Bayesian approach to the issue? Like, asking yourself how likely it is that the Patriots have been cheating for 7 years and no one caught them? Even though referees touch the ball (they have to spot it) every play and opponents have had every recovered fumble and Tom Brady interception in that time span to notice?

  • Another potential explanation for the lower fumble rate post-2006 could be this: it’s about that time that the Patriots offense became truly pass-happy. I suspect a higher proportion (maybe a MUCH higher proportion) of Patriots plays end with the ball-carrier (often, the pass-catcher) going out-of-bounds – as they run all these underneath, crossing, slant/flat patterns. Of course, there is practically zero risk of fumbling when you run out of bounds. So, if there is ‘% of plays that end up out-of-bounds’ data – it would be interesting to see if the Pats are also statistically ‘different’ from the rest of the NFL in this regard, too.

  • Deflate-gate will be remembered as one of the greatest learning opportunities in sports history, the media and millions of NFL fans will LEARN a lifelong lesson because of Deflate-gate.

    For example: Mike Florio @ProFootballTalk said on National TV right before the Super Bowl, that “they (footballs) don’t deflate on their own.” Nice try Mike, they actually do deflate (lose pressure, not lose air) on their own, because the air pressure of a football is a function of the temperature it is in. He must have forgotten his high school science class lessons where they proved the Ideal Gas Law (PV=nRT): The pressure of a gas (air) is a function of its temperature and volume, and is a Law of Physics.

    Bill Nye, the supposed science guy said the only way to take air out of a football was using a needle. Technically he’s correct, the needle takes air out/in, what he failed to mention was the air pressure of a fixed volume device like a football, basketball, soccer ball or a tire is a function of its temperature, and going from room temperature (approx. 72 degrees) to a 45 degree field at halftime does make a big impact on the air pressure in a football. Any football that started out at 12.5 psi will lose 1.38 psi, just due to the temperature change alone. This does not include vapor pressure loss, because air has water vapor in it which would cause additional pressure loss in a colder environment.

    Bill Nye was totally wrong and mislead the public when he spoke to GOOD MORNING AMERICA, trying to discredit Bill Belichick’s science saying: “rubbing the football, I don’t think you can change the pressure.” Totally FASLE, rubbing the football creates friction, and friction creates heat, adding heat changes the pressure of a football. It’s funny how the football coach was correct explaining the science and Bill Nye the supposed “science guy” was wrong, maybe he was just being a Seahawks fan. Nice try Bill Nye see the videos below proving your statements were incorrect.

    Sounds like because of deflate-gate Mike Florio, Bill Nye and so many others like: Troy Aikman, Mark Brunell, Cris Carter, Jerry Rice, Hines Ward, Jerome Bettis, Joe Montana, Mike Francesa, the New York newspapers, and the NFL will hopefully have learned these things since they misspoke on National TV and reported in the national media.

  • Even the NFL is just finding out that their rule/regulations for football pressure with a narrow 1 psi range 12.5 – 13.5 psi is IMPOSSIBLE to maintain when they measure at room temperature and then move the footballs on to a field where there is a 20 degree or greater temperature difference. Any football that started out in that range, will no longer be in that range, if it is taken into a new environment that is 20 degrees different or more (FACT). The NFL cannot have a rule regarding football air pressure, unless they also have a rule about the temperature and atmospheric conditions the measurements are taken in. Something they will surely have to fix and amend for next year.

    See Boston University “real science guy” Martin Schwaltz’s Pressure Calculator: Football deflation due to temperature change, he is way kool

    Google VIDEO of high school kids proving Ideal Gas Law works and the Patriots didn’t CHEAT

    Google VIDEO MIDE.COM TECHNOLOGY COMPANY proving footballs lose pressure when the temperature is lowered, thus the Ideal Gas Law works in the real world:
    The Laws of Physics are INDISPUTABLE and do not lie, cheat or know whose team is playing, this should have been pretty simple stuff to figure out from day one of this story.

    The Laws of Physics are INDISPUTABLE and do not lie, cheat or know whose team is playing, this should have been pretty simple stuff to figure out from day one of this story. It all says the same thing, no one CHEATED, just a lot misinformed people who didn’t know the Laws of Physics and that pressure of a gas is a function of its temperature.

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