Yes, the point is that merely being present at the scene of a crime, including this one, is not an offence.But that's not quite a simple as saying that the person who does nothing physical, does not himself use or threaten violence by word or deed, is innocent. He may be guilty because he is present in the group("present together") and he is helping or encouraging the violence or threat of it by joining, being or staying with the others.You can see how something threatening becomes so simply because of the numbers involved, even though many of them don't actually and in person utter a threat or physically threaten anyone.Of course, if someone happens to be in a group, some of them start the trouble and he instantly dissociates himself from wishing or being any part of it, but it starts up and goes on without him doing anything ,he wanting to discourage rather than encourage, he's entitled to be acquitted.We don't punish peacekeepers and those who think and behave as utterly peaceful and disapproving of the actions of others.