If you are trying to build muscle to improve your game on the field, pre- and post-workout nutrition is very important. According to new research, intra-workout nutrition (during your workout) also helps you to build muscle faster. The biggest problem that I see in middle school and high school athletes is inadequate overall eating habits. You can't be an elite athlete without giving your body the right fuel. These bad eating habits often follow you to your college team.
Your intra-workout nutrition could consist of a protein/carbohydrate drink that you sip during your workout.