[kosciusko51]

From ESPN:

An underinflated football could be easier to grip and catch. NFL rules stipulate that footballs must be inflated between 12.5 and 13.5 pounds per square inch and weigh between 14 and 15 ounces.

So an underinflated ball would weigh less than 14 oz., and have an internal pressure of less than 12.5 psi.

[kjam22]

Wet footballs weigh more etc. There are factors that can determine the weight of the football that happen during a game that don't have to do with inflation pressure. The guideline is to determine the TYPE of football. Its weight etc even when empty of air. Assuming they were using the right TYPE of football... the way to check the regulation during a game is with this...