Mark Lee Rollins for redOrbit.com – Your Universe Online
Even though it seems like it, this isn’t the first time football pressure or football contents have been called into question.
In 2012, USC was actually fined for intentionally deflating footballs.
This year, even, the Carolina Panthers and Minnesota Vikings were warned about modifying footballs.
Then go back to the 1976 Pro Bowl, there was a theory (since debunked) that the Oakland Raiders put Helium in their footballs for better hang time!
Regarding the recent allegations against the New England Patriots, according to ESPN, 11 of the 12 game balls were found to be underinflated by about 2 pounds each.
The NFL specifications say a football must be inflated to 12-1/2 to 13-/12 pounds per square inch.
However, the NFL does say the “Referee shall be the sole judge as to whether all balls offered for play comply with these specifications. A pump is to be furnished by the home club, and the balls shall remain under the supervision of the Referee until they are delivered to the ball attendant just prior to the start of the game.”
Some people have proposed the pressure drop was due to temperature. But the drop supposedly does not account going from 12.5 PSI to 10.5 PSI in 51 degree Fahrenheit weather for 90 minutes or so.
Most who test the temperature theory come up with a loss of 0.4 to 0.7 pounds, not the 2 pounds the NFL has said.
There’s also good Reddit post that posits the pressure could drop to as low as 11.8 psi due to changes from ambient pressure and temperature.
However, one of the most important parts of any measurement is the accuracy and the reproducibility of the measuring device. We at redOrbit were not able to divine the brand or accuracy of the gauges used by the NFL referees or officials, nor the techniques used to measure the pressure.
As for pressure gauges in general
According to Wikipedia, there’s a blanket statement that “accuracy of a typical mechanical (pressure) gauge” is ±3 psi. Higher accuracy gauges with ±1 psi accuracy can also be obtained.
This certainly explains the measurement discrepancy quite easily, but there are no references cited.
Some precision air pressure gauges are accurate to 0.25%, meaning a variation of +/- 0.3 psi. And these are for laboratory- or process-grade instruments.
Your more pedestrian, but still precision, tire gauges are designed to meet ANSI standards. ANSI (American National Standards Institute) has a standard ANSI B40.1 for pressure gauges. Grade D specifications, which is for inexpensive gauges that you might find for sports applications, has a mechanical accuracy rating of ± 4%.
Our conclusion/theory/product of overthinking (like the rest of this “scandal”)
So using 4% as our accuracy, we get (at 12.5 psi) a range of +/- 0.5 pounds. And multiple measurements by different devices compound an error, so it is possible that two or more measurements with different pressure gauges by different people could easily reach 1.0 psi of error, or more.
And don’t forget, assuming these are “dial type” gauges, there’s the end-user’s interpretation of what the pressure reads: “Is that 12.3 or 12.2 psi?”
So if you factor in temperature changes, device accuracy, measurement techniques, and interpretation by the reader, a variance of 2 pounds becomes infinitely more plausible.
Editor’s Note: Also check out NPR’s story on the science behind whether a deflated ball helps or hurts teams.
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