Studies have shown that most youngsters play for fun and would rather play for a losing team than sit on the bench of a winning one. You wouldn't think of yelling at a student in a classroom. Likewise, you should never yell criticism at a player, and instead should offer support. Likewise, they do not recognize the difference between athletic entertainment at the collegiate or professional levels, and educational athletics at the high school level, and how sportsmanship fits into the picture. Referees and other officials are trained to know and interpret the rules.
Opponents provide the most important factor of a game, the competition.
Often, the goal to win and attract a college scholarship overshadows the true purpose of interscholastic athletics. The pressure coaches and parents bring on athletes in this manner is unhealthy. Players and parents should know the penalties for breaking the rules, including acting in an unsportsmanlike manner. Sportsmanlike behavior, teamwork and improved performance are very important contributions to the team, and some of the long term values learned in educational athletics. All of these points are for naught if you don't shape proper behavior by setting a good example for others to follow.