Management of acute concussions is guided by consensus statement, and the return-to-play process begins when an athlete's symptoms and examination return to baseline. This process may be relatively clear if symptoms resolve within the normal time frame following a first or second concussion. This decision-making process is more complicated in an athlete with prolonged unresolved symptoms, multiple concussions both with and without prolonged recovery, or a structural brain injury. In these situations, determining when to retire an athlete after concussion is a complex decision, without available evidence-based guidelines. This article will discuss absolute and relative contraindications to returning an athlete to contact sport following a concussion in three separate scenarios: following potentially life-threatening brain injury, persistent clinical symptoms or signs of prolonged postconcussion syndrome, and multiple concussions but without residual symptoms or signs.