Woa there. If a gauge measures 13 psi within the football this is in addition to 14.7 psi atmospheric.
The pressure of 13 PSI is the pressure difference between the inside and outside. Adding 14.7 to 13 to get the absloute pressure inside the ball has nothing to do with it. A ball will burst if the pressure DIFFERENCE between the inside and outside is too large. If you reduce ambient pressure by 5 PSI, the pressure difference between the inside and outside will have changed by 5 PSI. That is the number you should look at.
If a ball can be inflated to 28PSI gauge pressure, then it will survive (in the case above).
A beach ball would not survive as large a change in pressure as a football, so deflating it would be sensible and easy.
On a flight I operated one day the Ccrew brought up a football and asked us about it. We were unable to deflate it and so we stuck it in a wardrobe cautioning the passenger that it might burst. At the end of the flight it was fine. I wouldn't want to be next to a bursting football, hence putting it in the wardrobe.
No one has yet mentioned that a ball will expand as the pressure inside increases. In this case it is likely to have a negligible effect though!