I would imagine the security will be just too intense for something to happen (I hope). A few years ago I was in Rome, so we went to a Serie A match. A couple of things that stuck out to me that there was flairs being lite in stands. Also the supporters from the visiting team were separated from the crowd by a good distance and surronded by full gear riot police. As for how can you stop jerks from throwing things, I am not sure there is an answer. They will always find something to throw. I guess spectatorless sports may be the answers, indeed sad.