I’ never played football at a level where game film is studied, so I don’t know, but I always thought sign stealing was one of the reasons you study game film. What plays a team runs, what plays a team runs when lined up in a particular formation, what plays a team runs in particular score and down situations, what plays might be triggered after particular player substitutions, ehat are the individual strengths and weaknesses of each individual on the other team and …what plays are run after specific sideline cues/signs. I see it is all educated guesswork. And I assumed every team would try to use decoy tactics to throw future opponents off. All a big shrug to me if you had asked me a month ago.