One of the scarier moments of my life came when my brother was an all star in little league as a 12 year old. The ball got smoked up the middle and his cap came flying off and he went down hard. I was playing CF (they had a couple of the older brothers helping them work out to get 9 per side for their games- and the ball went past me and rolled to the fence, as I wasn't playing it after seeing Matt go down like a sack of bricks.
Thankfully, it didn't hit his mellon, just the top of his cap- and he went down out of surprise/fear. The ball traveled an extra 140 feet (200 foot fence) after hitting his head. Could have killed him I think if it was 6 inches lower.
That Billy Wagner deal was brutal. It makes you sick to your stomach for a long time seeing something like that- especially when it's a friend/loved one down.