[greedo]

Network issues are most likely the problem, especially if the devices are issued by the NFL prior to gametime.

A coach needs a few things to really make this valuable. First they need a play chart for selecting the appropriate play call for the corresponding down and distance. This can be a canned application that doesn't require network connectivity after it's been loaded, but networking would allow an assistant to update the player personnel availability in real time so that you don't call a play with improper personnel.

The other thing the tablets replaced was the physical photos the teams used to use to review plays. The NFL previously made the teams use B&W photos sent down to the sidelines. They don't want the teams to use live replays for some reason, though the monstrous displays in most stadiums make this dumb.

So if you take out the network connection, these lose a lot of their value. I can't imagine a more hostile environment for Wifi than a stadium packed with a bazillion cellphones, plus goofy atmospherics due to design.