As it turned out according to the above documentary not only were those anti-war activists treated harshly outside of the convention - which was held at the now demolished International Amphitheater - also those delegates who weren't for VP Humphrey got some harsh treatment as well. A lot of drama was played out for TV back then and this type of drama is not what we see at political conventions anymore. Now with Donald Trump getting significant support in his bid for president it is possible we'll see drama at the Republican convention this summer.
Incidentally the last political convention held in Chicago was 1996 Democratic Convention at the United Center. Unlike this one where it was contested and one of the candidates from both parties will be a new president. The 1996 elections saw the incumbent "successfully renominated and re-elected President.
BTW, I'd be really amused to see if Chicago would ever host a Republican convention. I'm sure Chicago made a bid not long after the 96 convention and it never happened. Remember Chicago often held conventions for both parties at one point in time.
Also 1968 put a damper on Chicago hosting events like this with the harsh treatment of protesters and the drama on the floor. For those who witnessed this, it was likely a memorable election year.
I got to add Marathon Pundit's once favorite topic Bill Ayers - who at one time was associated with President Obama - was there at the 1968 convention. You will see him interviewed in the above documentary with a number of people such as WTTW's Joel Wiseman. And likely other well-known political figures for that time.