A “supplement” by definition is something you would take in addition to whatever you would eat or drink in the course of your normal diet. Examples of supplements can range from commonly used and safe substances such as multivitamins, to generally safe performance improving substances such as creatine, and then to unsafe items such as ephedrine and pseudoephedrine.
There is another class of substances beyond these called Performance Enhancing Drugs, which include anabolic steroids and human growth hormone. And yet another type of abused drug would include medications that are prescribed for proper medical reasons but are then abused and used in inappropriate ways. Ritalin, commonly used for attention deficit hyperactivity disorder, is reported to improve focus or cope with jet lag in athletes.
For the purposes of this post I would like to focus on substances that typically would not require a prescription. Unfortunately, that does not mean they are all safe, and in fact the most dangerous substances are surprisingly easy to obtain in your local community or on the internet. One of the biggest problems is that the supplement industry is unregulated so it is very difficult for the person using the supplement to be sure of the quality. Some supplements can contain a number of very unsafe ingredients.
Many young athletes are using and experimenting with substances supposedly useful to increase strength and muscle mass, improve endurance, and give them an edge on the competition. The pressures to use measures to improve sports performance are significant, and I expect these pressures only to increase as the years go by.
So let’s take a practical approach to supplements and let me provide a very simple “stoplight” guide to common supplements.
Read the full article at: Sideline Sports Doc

While not a 'supplement', water is very important component to good health.
Proper hydration with water -- not pop or sports drinks --
the night before a game and the day of a game/practice can make a positive impact on focus and physical performance.
According to the Mayo Clinic one symptom of dehydration is tiredness.
http://www.mayoclinic.com/health/dehydration/DS00561/DSECTION=symptoms