A trauma-induced alteration in mental status that may or may not involve loss of consciousness. 
Concussions may be characterized by one or more of the following frequently observed features:

• Headache

• Dizziness or vertigo

• Vacant stare (befuddled facial expressions)

• Delayed verbal and motor responses (slow to answer questions or follow instructions)

• Confusion and inability to focus attention (easily distracted and unable to follow through with normal activities)

• Disorientation (walking in the wrong direction, unaware of person, place or time, lack of awareness of surroundings)

• Slurred or incoherent speech (disjointed or incomprehensible statements)

• Nausea or vomiting

• Tinnitus (ringing in the ear)

• Sensitivity to light or sound

• Sleep disturbances (fatigue, sleeping more or less than usual)

• Observable lack of coordination (stumbling, inability to walk in a straight line)

• Emotions out of proportion to circumstances (out-of-place crying, distraught, overreaction)

• Memory deficits (repetitive questioning by the athlete, unable to memorize 3 of 3 objects or words in 5 minutes, serial 7’s, etc.)

• Any period of loss of consciousness