The result was that an influx of many thousands of fans through a narrow tunnel at the rear of the terrace, and into the two already overcrowded central pens, caused a huge crush at the front of the terrace, where people were being pressed up against the fencing by the weight of the crowd behind them. The people entering were unaware of the problems at the fence; police or stewards would normally have stood at the entrance to the tunnel if the central pens had reached capacity, and would have directed fans to the side pens, but on this occasion they did not, for reasons which have never been fully explained.
For some time, the problem at the front of the pen was not noticed by anybody other than those affected; the attention of most people was absorbed by the match, which had already begun. It was not until 3:06 pm that the referee, Ray Lewis, after being advised by the police, stopped the match several minutes after fans had started climbing the fence to escape the crush. By this time, a small gate in the fencing had been forced open and some fans escaped via this route; others continued to climb over the fencing, and still other fans were pulled to safety by fellow fans in the West Stand directly above the Leppings Lane terrace. Finally the fence broke under pressure of people.
The fans were packed so tightly in the pens that many died standing up of compressive asphyxia. The pitch quickly started to fill with people sweating and gasping for breath and injured by crushing, and with the bodies of the dead. The police, stewards and ambulance service present at the stadium were overwhelmed. Uninjured fans helped as best they could, many attempting CPR and some tearing down advertising hoardings to act as makeshift stretchers
