It goes without saying that some contact sports are especially brutal and can cause serious head injuries. In fact, the sport of boxing traditionally has as the ultimate goal of a prize fight a “knockout”, which is when one fighter is punched in the head so hard that it brings about a concussion. Other sports, such as hockey and American football, also see their fair share of head injuries, and in some ways, these injuries can be even more dangerous over the long term. In both hockey and American football, players wear helmets to protect their heads. While the helmets may protect well against bone fractures of the skull, they do not and cannot fully protect the brain. This organ is made up of very delicate tissue, making any trauma to it serious. To understand why a concussion occurs is a matter of physics. One must remember that the brain is encased in the skull, and in between the brain and the skull is fluid that acts as a cushion. When the force of a hit to the head is so extreme, this cushion is unable to do its job, and the delicate tissue of the brain actually hits the skull. This causes bruising on the brain, often causing immediate consequences that are easy to recognize. A person who is concussed will be disoriented, often unable to answer simple questions such as, “Where are you right now?” In the most extreme cases, the person suffering a concussion will be completely knocked out, meaning he has lost consciousness altogether.