To answer your question, the evidence I have is his own words from the police interview as quoted in the news article. Have you read the articless on this?

From KSL: "In an interview, Gardner told police that he was upset about how the game ended with BYU defeating the University of Utah, 22-21. "Gardner saw people throwing water bottles and he was so mad that he threw one in the direction of the cheer team."

So he wasn't just throwing a bottle randomly as you claim - he admits he was aiming at the cheer team. Sadly for him, he had better aim than the other people throwing the bottles.

Further from the article on his interview with the police: "Gardner admitted knowing that throwing a water bottle from that height could injure someone".

So he freely admits he knew if he hit someone with a bottle thrown from that height it could injure someone, and chose to deliberatly aim it at the BYU cheer team anyway. Knowing that if his aim was good, someone was going to get seriously injured.

Those are the facts as he admits them. Lets at least be honest about what he did.