Riot police were called in to tackle crowd chaos at a World Cup fan zone just as the tournament kicked off. Tens of thousands of fans pushed and shoved against police lines to enter a secure area. It came as fans were queueing before Qatar's 2-0 defeat to Ecuador, shown on giant screens at central Doha's FIFA fan festival.Helmeted cops armed with batons and shields stood guard at the entrance and pushing and shoving broke out as crushed fans pleaded to enter the zone.