A traumatic brain injury is any damage to the brain. My son was in a car accident, passenger in the back seat of car. Another car ran stop sign, the driver of the car my son in tried to avoid the collision and went off the road into a concrete drainage ditch. The driver died. The front seat passenger had a twisted ankle.
My son needed emergency to the frontal lobe of his brain, because his brain had been shaken inside is skull upon impact.
It is going to be caused by an accident. I do not know of any normal conditions that would cause one.