Skaters from the Stockholm Roller Derby work out during a practice session before their women's flat track roller derby bout against the Kallio Rolling Rainbow in Huddinge June 9, 2011. Flat track roller derby consists of two teams of five players each and points are scored when the assigned scorer or 'jammer' laps members of the opposing team. Picture taken June 9, 2011. REUTERS/Bob Strong (SWEDEN - Tags: SPORT SOCIETY)