The accounts I have read of people on both "sides" naturally reflect their own point of view - the fascist groups claiming that the anti-fascist groups used violence against them, and vice versa, and it is a fact that there are always people in every protest group who overstep the mark.
Most of the accounts I have read, from protesters and journalists who were present, refer to the fact that the police did very little to pre-empt or stop the violence between the groups.
I agree that on both sides there are no doubt people who go along to these things with the express intention of inciting violence and participating in it. This is, of course, completely wrong. It is also counter-productive because it loses public sympathy and support. I tend to think they don't really care about that because they are just violent individuals who use their membership of a group as a cover for their violent natures. In my view, any person that resorts to violence discredits their cause and should be arrested.
However, I think driving a car into a crowd of protesters is in a completely different league. If you have the protection of a car and so have the means to protect yourself by driving away but instead drive it into a crowd of protesters, you know you will kill or seriously injure some of them. In this scenario the man did this because he hated them for what they were and/or what they believed in. That is surely a terrorist attack. Had the same action been carried out by a black member of a left wing group, I wonder if Trump would have been more forthcoming in his condemnation of the ideology and behaviour of the group of which this young man was a member.