Nearly 40 years ago, Gronwall and Wrightson1,2 first raised concerns about cumulative brain injury with repeated concussions. More than 25 years ago, when I published the first return-to-play guidelines for after a concussion, I stressed the need for further evidence-based research in this area.3 Since then, there have been 4 international concussion in sport conferences with published consensus statements, initial and updated concussion statements from the National Athletic Trainers’ Association and the American College of Sports Medicine, and a recent concussion statement from the American Medical Society for Sports Medicine.