Game-Time Communications

I am a coach of a high school varsity lacrosse team. Our club has only been in existence for 3 years, so that is the maximum amount of time that any of my girls have played. We are really good about communication in practice, but as soon as the whistle blows to start a game they all clam up. There is little to no talking on the field. This causes us to have breakdowns due to communication during games and thus we lose.