If you haven't heard already, there was a riot at an Egyptian Premier League football match on Wednesday, February 1st that reportedly left at least 70 people dead and a thousand more injured. As of now I haven't uncovered why fans of the home side, Al-Masry stormed the field with stones, bottles, fireworks and the like after Masry won the match against the best team in Egypt, Al-Ahly, 3-1. After the match was over, fans of the home side stormed the field and chased players and fans of Al-Ahly, you can see the scene on the footage I've posted from YouTube above. The staff and players of the opposing side had to flee the field once the riot began, and an Al-Ahly manager had to be rescued while being beaten by home fans.
Whatever reason the fans have for such a display is really no reason at all. Certain news outlets have hinted that the riot could be linked to recent political unrest, but it looks like no one knows for sure.
I encourage you to search for more videos and articles covering this unfortunate incident as they may be able to tell the story better then me.