David D Kirkpatrick in Cairo for the New York Times has included some points on the cultural details:

[....] The mayhem also focused renewed attention on the potential savagery of organized groups of die-hard fans, known here as ultras, who have emerged as a volatile component of Egyptian politics in the year of turmoil since Mr. Mubarak left power.

Previously apolitical, the ultras were known for their rowdy behavior, obscene chants and apparently endless enthusiasm for clashes with the often-brutal Egyptian police. “ACAB,” one group of Cairo ultras likes to spray-paint on city walls, standing for, “All Cops are Bastards.”

The ultras joined the revolt against Mr. Mubarak on the first day of protests, taunting and harassing police as they tried to crack down on thousands of other marchers heading for the Cairo’s Tahrir Square. Protest organizers said they played a more central role in the so-called “battle of the camels,” helping beat back mobs of Mubarak supporters, some of them riding camels, in a daylong battle of rocks and Molotov cocktails.

Since then, however, the ultras have injected an unpredictable element of chaos into the frequent demonstrations over the course of the political transition here. They drove an assault on the Israeli Embassy [....]

"Blood sport" history:

In August, 2011, FP looked back at some of the notable occasions when political violence has spilled over onto athletic playing fields.

http://www.foreignpolicy.com/articles/2011/08/19/blood_sport