“A direct blow to the head, or a blow to the body that suddenly rotates the head, can lead to a concussion, causing the brain to rapidly move back and forth inside the skull. “You don’t need impact to the head to have a concussion,” Dr. Sethi notes. For example, a football tackle or a fender bender may involve no head contact but could cause the head to whip around fast enough to cause a concussion.

Concussions typically do not damage the brain. “In the majority of cases, CAT-scans of concussion come back negative,” Dr. Sethi says. Yet, a concussion can temporarily stop the brain from working properly.

The danger is in not recognizing the signs of a concussion, especially since they are not always obvious, Dr. Sethi stresses. “Parents should know that concussion symptoms—a headache, dizziness, difficulty tolerating light or noise–could be very subtle,” he says. Athletes who have sustained a knock to the head commonly insist that they’re fine so that they can keep playing. “If you’re a coach on the sideline you may not notice anything wrong until you see that a player is off balance, looks confused or disoriented, or has a glassy look in his eyes,” he says.

Even severe head injuries, like hematomas, do not always produce immediate symptoms, Dr. Sethi says, recounting the late actor Natasha Richardson, who fell off her skis and hit the back of her head, insisted she felt fine, and refused medical care. “We call these injuries walking, talking, and dying. By the time she got to the hospital, her brain was hemorrhaging.”

Weill Cornell Medicine (https://weillcornell.org/news/national-winter-sports-traumatic-brain-injury-tbi-awareness)