What is the correct inflation pressure?
Is 2 psi low 1%, 10%, or 50%?
Minimum allowable psi is 12.5. It has been reported that 11 footballs were 2 psi below the minimum and that would be 16% variance.
NFL rules state 12.5 to 13.5 psi is the allowable range.
2/13=15.3%
Correct pressure is 12 1/2 to 13 1/2 psi. If they were all at least 2 psi under (or 10 1/2 psi) that’s 23% under the average pressure of 13 psi. So if it’s only 3/4’s of the regulation pressure, I would expect the ref’s to notice it.
A 2 psi deficiency (10.5 psi) would be quite noticeable by anyone handling the ball, including the game officials.
"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."
A game official handles the football immediately prior to each play. If there was a problem, it could and should have addressed it before or during the game.