The number of dead in Sunday's football (soccer) riot/clash with police in Cairo is now at least 30, the worst soccer violence since the Port Said clashes that took 70 lives in 2012. After that event, the authorities banned spectators from attending matches for some time, and were just beginning to relax that by selling only 5000 tickets to this match between Zamalek and the ENPPI Club. Many non-ticketholders tried to rush the stadium gates, and the rabid Zamalek supporters known as the Ultras White Knights clashed with the police. Since the match was at the military-owned Air Defense Forces Stadium, the Interior Ministry says the police were protecting public property.
For further reading, James M. Dorsey's The Turbulent World of Middle East Soccer, the go-to site for the Ultras and their clashes, as usual provides a clear account, with necessary background, of what is known so far.
For other coverage, see Ahram Online accounts here and here, and Zeinobia's blog offers both commentary and some photos and video.