I know people have said the crowd yelling can be a form of giving info, but whats stopping a team from having someone in the crowd hold up one hand if the other team is going a and the other if a team is going b. There's a bunch of ways to do this you could even have signals or multiple people. Obviously a stage setup makes this harder, but in an arena where there are fans all around you could setup fans across from you and have them do it.