The Hillsborough disaster was a fatal crowd crush at a football match at Hillsborough Stadium in Sheffield, South Yorkshire, England, on 15 April 1989. It occurred during an FA Cup semi-final between Liverpool and Nottingham Forest in the two standing-only central pens within the Leppings Lane stand allocated to Liverpool supporters. Shortly before kick-off, police match commander David Duckenfield ordered exit gate C to be opened in an attempt to ease crowding, which led to an influx of supporters entering the pens. This resulted in overcrowding of those pens and the fatal crush; with a total of 97 fatalities and 766 injuries, the disaster is the deadliest in British sporting history. Ninety-four people died on the day; another person died in hospital days later, and another died in 1993. In July 2021, a coroner ruled that Andrew Devine, who died 32 years later, after suffering severe and irreversible brain damage on the day, was the 97th victim. The match was abandoned and restaged at Old Trafford in Manchester on 7 May 1989; Liverpool won and went on to win that season's FA Cup.

Crowd collapses and crowd crushes are catastrophic incidents that can occur when a body of people becomes dangerously overcrowded. When numbers are up to about five people per square meter, the environment may feel cramped but manageable; when numbers reach between eight and ten people per square meter, individuals become pressed against each other and may be swept along against their will by the motion of the crowd. Under these conditions, the crowd may undergo a progressive collapse where the pressure pushes people off their feet, resulting in people being trampled or crushed by the weight of other people falling on top of them. At even higher densities, the pressure on each individual can cause them to be crushed or asphyxiated while still upright.