For those who don't know and those too young to remember this is what happened at Hillsborough:
Most football grounds in 1989 had fixed metal fencing at the front of stands (between the crowd and the pitch) due to hooliganism in football. Sturdy, solid stuff. Grounds had standing areas rather than the all seater stadiums we now have in football - essentially really wide, concrete steps with the odd metal railing here and there and fixed, concrete sides. So basically, you had an enclosed space with fixed boundaries, and tiny entrances/exits. Because of this, the numbers allowed in had to be watched very carefully, as unlike now it wasn't a case of one person for every seat and then it's full. There was the potential for overcrowding and death.
Hillsborough was a big ground that was used for FA cup semi final matches. It was chosen for capacity and it's ability to host big matches (it was neither teams home ground.)
The police were manning the entrance to the stands. There were a lot of Liverpool fans who had been stuck in traffic and so, just prior to kick off, lots of people were trying to get into the ground through a very small entrance, resulting in a big mass of people outside the turnstiles.
The police took the decision to open gates into an already full area to ease the build up. People flooded in. Those going in had no idea of the situation in the stand as they had no view of it as they entered the gates. Those already in the stand were pushed forward by the flow of people into the metal fencing. They were being crushed to death. People continued to pour in.
And it was the fans who realised what was happening. It was the fans who tried to save their fellow fans lives
96 died. Hundreds more were injured.