Think about it. When the pitcher throws a ball toward a batter's strike zone, only a small error in aim could cause it to hit the batter's head. And remember that part about how a fastball can go over 100 miles per hour (160 kilometers per hour)? Well, just think for a moment about how fast a batted-ball can travel. Imagine what it feels like to have an object traveling that fast impact your face. It could knock your teeth out, blacken your eye or even crack your skull. Unlike players in more violent sports, such as football and rugby, unless they're at bat, baseball players don't wear any more head protection than a thin cap. So if that ball connects with your head while you're out in the field (or even on the bench), there's really nothing standing in its way.
Getting hit in the head with a ball isn't the only way to sustain a head injury in baseball. Outfielders can bump into one another, runners can collide with catchers -- the possibilities for a blow to the skull are endless. And a blow to the skull can lead to a concussion. The major symptoms of which are nausea, dizziness, headaches and confusion. Head injuries shouldn't be taken lightly and if concussion is suspected, a trip to the emergency room is in order.