It's theoretically possible for McNally to be a football-deflating savant and be needling each ball for 1 second extremely quickly, but to believe this to be the case would mean you'd be pulling a Wells and only believing half of Anderson's memory and working off the Non-Logo gauge, and even then, all the other contributing factors to potential PSI loss go a very long way toward showing the resulting levels at halftime were simply due to nature and in-game factors.
I can fully see a scenario where Brady puts the fear of god in Jastremski after a bad PSI day (i.e. Jets game) who then berates McNally that the balls better be right or Brady will flip out, causing McNally to just let a little air out before games thinking it'll keep Brady happy. However, this still does not give any indication that Brady was part of the operation, and all of it could simply be a byproduct of his overly intense persona at times.
And even then, if you were to only believe half of Anderson's memory, believe none of the in-game factors made much difference, AND believe that Brady caused ball deflating to occur either by direct command or indirect rage, what you're left with is one dude needling a ball for a second. This is $25k fine material and that's it.