If the Colts player could tell the ball was under inflated, why didn’t Brady notice that. Tom Brady is the quarterback, and the most expert about noticing the inflation size of the ball.
My only guess is that he knew about the cheating, or noticed that the ball was under inflated, and did not report it.
Either way, it appears to me that Brady is also a cheater.
Brady is on record that he prefers an underinflated ball.
http://profootballtalk.nbcsports.com/2015/01/20/brady-said-in-2011-he-likes-deflated-footballs/