Concussion researchers have recognized a new concussion sign that could identify up to 33% of undiagnosed concussions. After a hit to the head, individuals sometimes quickly shake their head back and forth. Although it has been depicted in movies, television, and even cartoons for decades, this motion has never been studied, named, and does not appear on any medical or sports organization's list of potential concussion signs. A new study says it should. The study reveals that when athletes exhibit this movement, named a "Spontaneous Headshake After a Kinematic Event" or SHAAKE, athletes report they had a concussion 72% of...