This can be a complicated issue because it depends on your sport, the duration of symptoms of your concussion, and your personal concussion history. It is best to see a physician who is well trained in sports-related concussion to answer this question on an individual basis.
However, assuming this is your first concussion and your symptoms resolve within one week, there have been published recommendations by an expert panel that outlines a graded return to play based on symptoms. The important concept here is making sure that your concussion has completely resolved prior to returning to play. This ensures that you will not worsen your current concussion and also prevent what has been called "second impact syndrome", where a second, lesser concussion leads to generalized brain swelling and death. The protocol below is in place because while your symptoms may be gone while at rest, they may resurface with physical activity. It works like this:
Step 1: Wait for symptoms to totally resolve. This means total rest from physical and mental activity (sometimes we'll have kids stay home from school during this period if their schoolwork is affected and they have symptoms during class or while doing homework).
Step 2: After 24 hours of being symptom-free, you can try light aerobic exercise (jogging, stationary bike).
Step 3: On day 2, you can try sport-specific exercise, such as running drills in soccer, football, or basketball, or skating drills in hockey. No head contact.
Step 4: On day 3, perform non-contact training drills at higher intensity and complexity, such as running patterns in football, dribbling and passing drills in soccer and basketball. Again, no head contact.
Step 5: On day 4, you can participate in full contact practice.
Step 6: On day 5, you can go back to full contact game.
This progression should be supervised by someone fully versed in this protocol and knowledgeable in sports concussion. Most state high school athletic associations as well as the NCAA have adopted this program and also require medical clearance by a physician before progressing to step 5. If at any time you have symptoms of your concussion during this progression, you should go back to the previous step.
If your symptoms last longer than one week, or this is the second concussion within 3 months, or you have had more than 3 concussions within a year, you should definitely see a physician with special training in concussion management.