how did the Hillsborough disaster start?

The Hillsborough disaster was an incident that occurred on 15 April 1989 at the Hillsborough Stadium in Sheffield, England, during the FA Cup semi-final match between Liverpool and Nottingham Forest football clubs. Entry to the ground was slow due to the few decrepit turnstiles available to the Liverpool fans which caused dangerous overcrowding outside the ground before kick-off. In an attempt to ease pressure outside the ground, Chief Superintendent Duckenfield ordered an exit gate to be opened. The opened exit gate led to a tunnel marked "Standing" which led directly to the two already overcrowded enclosures (pens). In previous years the tunnel had been closed off by police when the two central pens were full, however on this occasion the tunnel was unmanned.

The ensuing influx of supporters caused crushing and some fans climbed over side fences or were lifted by fellow supporters onto the stand above to escape the crush. Moments after kick-off, a crush barrier broke and fans began to fall on top of each other.

It wasn't a riot