In Mecca, Saudia Arabia, 35 are trampled to death in a stampede of pilgrims during the ritual of Stoning the Devil. The ritual Stoning the Devil is one of the most dangerous parts of the entire Hajj and is when most of the safety problems occur.
One problem is that crowds increase every year, especially with long-distance travel becoming cheaper, easier, and more accessible to more people. Another problem is that many Muslims believe the Stoning the Devil ritual needs to be performed right after noon prayers, but scholars say it can be done any time during the day.
Third, this takes place on the last day of the pilgrimage when people are getting very tired. Finally, too many pilgrims ignore instructions from those responsible for public safety, making a difficult situation dangerous.