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More than anything else, that one piece of information will help us figure out how the balls could have deflated.
NFL game balls must be inflated to between 12.5 and 13.5 pounds per square inch. The Patriots inflate their game balls to 12.5 PSI, according to Bill Belichick and Tom Brady.
Two hours and 15 minutes before kickoff, New England's game balls were measured and approved by the referees, presumably at 12.5 PSI. When they were measured again at halftime, they were found to be under-inflated. Indianapolis' game balls were also measured at halftime, but they were within regulations, according to widespread reports.
According to ESPN's Chris Mortensen, those Patriots balls were two pounds per square inch below the minimum of 12.5 PSI allowed under NFL rules. But that has not been confirmed by the NFL. Mike Florio of ProFootballTalk reports that a source told him only one of the 11 balls was two PSI below the limit, and the other 10 were under-inflated by by around one PSI.
The Patriots claim that the balls deflated naturally as a result of the weather and the "rubbing process" that the team uses to get them ready for the game. Belichick said at a press conference that the balls can lose as much as 1.5 PSI as a result of those two factors (he also noted that the ball re-inflates by 0.5 PSI when it's brought back indoors to be measured, resulting in a net difference of one PSI).
When you run the math, it would have taken a 40-degree temperature change to result in a two PSI deflation. Since the temperature never dipped below 47 degrees during the game, it wasn't cold enough for the weather to deflate the balls two PSI. However, if the balls were only under-inflated by one PSI, the weather theory is plausible.
There's also this monkey wrench in New England's explanation: Why were the Colts' balls fine?
If natural factors were to blame, all balls exposed to the same conditions would deflate uniformly. So why wouldn't Indianapolis' game balls be under the 12.5 PSI limit as well?
The answer comes down to our original question: how much under 12.5 PSI were the New England game balls?
If they were one PSI under the limit, then it's possible that Indianapolis' game balls were originally inflated to 13.5 PSI, and then fell to around 12.5 PSI - still within the legal range - when they were measured at halftime.
But if the New England game balls were two PSI under the limit, then the Colts balls would have also been below the legal limit if natural factors were responsible.
The Patriots have denied any wrongdoing at every turn. Owner Robert Kraft essentially dared the NFL to prove they tampered with the balls, and demanded an apology from the league if they can't.
The NFL says it will take the league several more weeks to complete its investigation. Once we get those numbers, we'll have a much better idea of how this could have happened.