“Or, better yet: Ideal Gas Law”
The Ideal Gas Law dos not apply because none of the gasses that we are discussing are ideal gases. Oxygen comes the closest, nitrogen is far away from it. CO2 is even further away.
An “Ideal Gas” in this context would be one who’s vapor pressure would reach zero when the temperature was absolute zero. That would make the pressure for delta T linear.
And no gas, in that context, is an Ideal Gas.
I have my chem eng degree and pro license and experience in various industries working on the situation. So far it appears that there is much to do about what and how natural conditions and causes could affect a manufactured object that is about to be tossed about and kicked about. It would be very difficult to strictly apply the ideal/perfect gas law(s) to a football. A person might throw in some of the fudge factors developed over years of research but it seems to me that trying to make a court like case for use of an inflatable ball that has been subjected to specified reasonable conditions is a bit too much.