High decibel white noise. Rock music full blast. Prerecorded cheering. NFL coaches have always found a way, in the days leading up to a road game, to simulate the environment at an opponent’s stadium. Now, they use crickets.
Some NFL stadiums are louder than others, but every one of them, depending on the point in the game, can generate enough noise to make it impossible to hear the person next to you. For this reason, offensive football involves a variety of hand signals and silent snap counts. There are so many routes and route combinations that you really can’t get hand signals for all of them, which means, in a hostile environment, your ability to change the play is limited to whatever hand signals you have, and, more specifically, whatever hand signals you can remember.