Three major types of brain injuries are closed, penetrating, and nontraumatic brain injuries. Closed brain injuries occur when the skull is left intact, and the brain is injured through violent impacts against the skull. They may be the result of repeated blows to the head or from one single traumatic strike. Boxing, football, and other sports often lead to TBIs as well as car and bicycle accidents. Penetrating injuries occur when the skull becomes exposed, and the brain is pierced. Bullets and any other object moving with sufficient force can pierce the skull and damage the brain. The brain may also be damaged through the eye, which can be prevented with the use of safety goggles. A non-traumatic brain injury is typically caused by forces from within the body, such as serious health conditions and events. Strokes, seizures, tumors, lack of oxygen, and exposure to neurotoxic poisons can all cause non-traumatic brain injuries. Although no trauma is involved in these types of brain injuries, their consequences on victims can be just as dire.