It’s illegal for teams to use electronic means to record from the coaches box, the sidelines, or (one other place - the locker-room, I think). Apparently one can use Polaroids, or do it from a place other than one of the three proscribed locations, or with personnel not employed by the teams.
I know a couple of years ago there was an issue with one team apparently having gotten film of signals from one of the broadcasters - including footage not broadcast.
Thank you.