The standing area of Leppings Lane was granted a capacity of 7,200 and it was decided later a safe figure should have been 5,425. 2,900 fans also accessed the corner stand from the 7 turnstiles at the back. It was a death trap and the only reason this hadn't happened sooner was because of careful planning from the previous match commander who did not meet with David Duckenfield.
People can speculate that the fans were to blame all they want. The street access to the stand was a constricted bottleneck and as has been mentioned, an accordion effect can occur in these situations which can account for the crushing outside the stand. Excess drinking or numerous ticketless fans as far as i'm aware has not been proven. It certainly is not the cause of what happened which some have suggested.