Six months off may not be long enough for the brains of football players to completely heal after a single season, putting them at even greater risk of head injury the next season. "I don't want to be an alarmist, but this is something to be concerned about," said the lead researcher. The analysis revealed that white matter changes in the players' brains started to look different from the control group when players experienced as few as 10 to 15 head impacts.