What situation constitutes illegal substitution and what is the resulting penalty?

The situation that constitutes illegal substitution occurs when there are too many players on the field at the snap of the ball. According to NFHS football rules, a team is only allowed to have 11 players on the field during a play. If a team has more than 11 players on the field, it results in a penalty for illegal substitution, which is a 5-yard penalty.

This rule is designed to maintain fair play and ensure that teams operate within the specified limits. The enforcement of the penalty helps to discourage teams from attempting to gain an advantage by sending in more players than allowed, which could disrupt the flow of the game and create an unfair situation for the opposing team. Thus, the correct answer reflects the principle of maintaining a level playing field in the sport.