Could also be this, which seems more likely coz it is exactly what happened in the Hillsbourough disaster
https://www.trueprepper.com/crowd-crush-lurking-danger-crowds/
Crowd Crush
The Lurking Danger of Crowds
August 26, 2016 Rusty Collins Article, Personal Safety, Prepping Article
Fairs, sporting events, religious gatherings- many great events are gatherings of crowds. Parades can entertain, church gatherings can inspire, New Year’s Eves around the globe cause us to reflect and look forward to the future. But all of these crowded events have a significant danger brimming just under the surface. We often think about stampedes when thinking of crowd injuries, but crowd crushes can be much more deadly on a larger scale.
What are the Dangers of Crowds?
Crowded places present all kinds of dangers. Petty crime, becoming lost, and trampling just to name a few. Trampling is common during disasters where crowds are running away, but crowd events can be even more dangerous. When the density of a crowd reaches certain points, it behaves less like a group of individuals and more like a fluid. This can cause ‘crowd crush’ and ‘crowd collapse’- both extremely dangerous phenomenons. As recently as 2015 over 2000 people were killed in a single event due to the effects of a crowd crush.
Cant find the link re science quickly but if remembered correctly 5/6 peeps per square meter in a funnel situation can start it and it is impossible to stop as the pressure flows to the point of the greatest density in the funnel