That's actually a different demo (this past Saturday, whereas the one I started this thread over occurred two weeks earlier). That's OK, as I attended the one your link concerns as well, so here goes ...
I estimate the crowd of counter-demonstrators at slightly fewer than 200 (not "hundreds"), of whom the majority seemed to be from Jews For Justice In Palestine, and most of the rest from Antifa. The rally began with a Bernie Sanders supporter telling the audience that the organizers believed in free speech and were allowing him to speak even though they disagreed with his leftism. Other speakers denounced white supremacism as an attempt to deny minorities their Constitutional rights. At the end of the rally, the counter-demonstrators were invited to send a representative to speak, but noone took them up on the offer. I witnessed an altercation between counter-demonstrators and the police from a distance, but didn't really see very much, so I can't comment on who started what.
After the main rally at Parkman Bandstand, the rally adjourned to the statehouse steps at Park and Beacon, where I got to see the free speech proponents up close. One guy that caught my attention (considering my own Prussian ancestry) was carrying a Prussian flag, wearing a Prussian helmet, and carrying a sign reading "Make Germany Prussia Again!" The Antifa people tried to crash the second rally, but were blocked by police using their bikes as barricades. With the second rally finished, everyone went home.
One thing worth noting was a rally off to the side of the main event by the Progressive Labor Party, who were calling for class struggle. Although I have no sympathy for that hard-line Stalinist group, they seemed to share my sensitivity to the bourgeois liberal bent of the so-called "far left" of today.