"Hundreds to thousands of head impacts may cause some sports participants to have mild to severe neurological problems later in life. That's probably not the answer people want, but it's the current state of the science. One problem is there are a number of factors that can influence how someone responds to head impacts. Some of these factors include injury history, head impact exposure (e.g., number and magnitude), and genetics. The clinical usefulness of this information, however, is still not completely understood."