This is the key. A capped bottle even if soft plastic like those cheap water bottles has a chance to to some damage. An open one will lose some volume in the air and will evacuate whatever is left on impact.We sit right next to the student section and the empty fireball shooters have rained down all season.
This weekend there was a LOT of uncapped water bottles and I’m sure some people got soaked.
That said, you sit by the students you have to expect a little chicanery and I don’t want anything to happen that could impact student enjoyment. I knew people would complain but I never actually saw a full, capped bottle flying.
I am not condoning it but the risk here is minimal.
At my high school we had a girl end up in the hospital after our class threw their mortar boards (graduation caps) into the air. She caught a corner in the eye. Those are more dangerous but my point is that the risk is never zero.