You know, I remember when I was a teenager I worked some summers at a concert venue. I remember I was hanging out with some other employees a few hours before the gates opened, and I happened to have a full Dasani water bottle. The cap was still on and it was sealed.
One of the supervisors was shocked I had a capped water bottle, and told me to get rid of the cap immediately. She was in a panic.
It was that moment when I learned that filled, capped water bottles are, for all intents and purposes, weapons. They can do some real damage to an artist on a stage... or in this case a cheer coach on the field.
I hope they find and punish the guy who did this.