The vast majority of sports riots are initiated by fans of the winning team, and usually on their home turf. Jerry Middleton Lewis, a professor emeritus of sociology at Kent State University who has studied sports fan violence since 1960, dubs this type of incident “celebrating riots.” In his book Sports Fan Violence in North America he writes that, “the typical celebrating sports riot is located either on the playing field or the court after the winning of a championship.”

Why? Psychologists have long understood that spectators whose teams win experience a spike in testosterone, a hormone associated with aggression, while those whose teams lose suffer a commensurate plunge in the hormone. Researchers at the Violence Research Group at Cardiff University conducted a survey of rugby supporters entering and leaving a professional soccer venue in Wales, and found that fans whose teams had just won described themselves as feeling more aggressive than losing teams’ fans did.

The testosterone effect is especially strong when teams with a long history of fierce opposition play one another, and when the game in question is particularly close. The Port Said riot took place after a game between historic rivals El Masry of Port Said and Al Ahly of Cairo. The violence erupted after El Masry came from behind with a string of goals and won with a final score of 3-1. The hometown supporters flooded onto the field, attacking the other team’s players and its fans with knives and clubs.