That a mob formed and acted as one is a main reason that police need to manage 2000 people in an space.
Violent agents will always make their way to the front of any conflict zone as that is where they find the oppertunity to be violent.
Humans are like any animal that live in community groupings and will engage in "herd instinct" in large crowds.
Going with the flow, and allowing others to make (sometimes vital) decisions on how they move within a crowd.
Crush deaths are always a risk in crowds as FOMO creates the danger
Mismanagement of about 400 people on a night out in NI killed 3.
https://www.irishtimes.com/news/ireland/irish-news/tyrone-disco-deaths-it-started-with-pushing-then-the-crushing-started-1.3830279
^ includes an account of a girl who was pulled out
https://www.google.com/amp/s/news.sky.com/story/amp/two-men-to-be-charged-over-deaths-of-three-teenagers-in-crush-outside-st-patricks-day-disco-12686942
Note ^ how the NI police investgated its own actions on how it managed the result of the crush. The two who should have done proper planning are charged.
And NI was a "happy" crowd
Add in even a few violent agents and rioting and the risk of an accidental stampede goes through the roof.
The police planning was poor if 2000 people were turning up with the aim of "stopping hate" and stopping women from meeting and speaking at a fixed focal point.