A tragic weekend for Nigerian football got even worse when clashes between rival cult factions left at least 13 people dead, some of whom were supporters of Premier League club Ocean Boys.Club officials refused to speak about the incident and most have had their cell phones switched off since Saturday.The clashes, between rival gangs Greenlanders and Highlanders are believed to have started on Friday, when a member of one of the groups, who is an Ocean Boys supporter, was gunned down in Yenagoa, the capital of the oil-producing Bayelsa State.A reprisal attack was launched at a night club later that night which left a member of the rival gang dead, escalating the situation and leading to an attack on the bus carrying Ocean Boys supporters to their league game against Bayelsa United in Ughelli, in Delta State.Seven persons died instantly while three others died later.The game went ahead on Saturday with Ocean Boys beating city rivals and league leaders Bayelsa United 1-0.Source: Kickoff