Athletes at the youth and high school level should not be allowed to return to play in the same game or practice even if all post-concussion signs or symptoms clear, because of the risk of second impact syndrome (SIS), which occurs when an athlete who sustains head trauma, i.e. a traumatic brain injury - often a concussion or worse injury, such as a cerebral contusion (bruised brain) - sustains a second head injury before signs of the initial injury have cleared.  It is preferable for athletes suffering even a mild concussion not to return to play for at least one week in order to allow time for evaluating and treating the concussion and for the brain to heal.