Many Russians are unfamiliar with rugby

The Russian news agency RIA said police had received a tip-off about a mass brawl at an empty sports ground on the city's outskirts.

Nearly 100 people were involved - either playing or watching the match.

When the police realised no offences had been committed the detainees were all released, RIA said.

The police argued that their action - involving 73 officers - was justified because they had not been told in advance about the match.

The players were quoted as saying such amateur matches were common and were often held in the neighbouring Volgograd and Stavropol regions of southern Russia.