Leeds United F.C.–Millwall F.C. rivalry

The rivalry between Leeds United and Millwall is a North–South divide rivalry in English football. Millwall were founded in London in 1885 and Leeds United in Yorkshire in 1919, over 170 miles (270 km) apart. Both sides entered the Football League in 1920–21 season, albeit in different divisions. From 1920 to 2003 the sides met just 12 times; competing in different tiers for the majority of their histories, and neither considering the other a rival on the pitch. From 2004 to 2020, the teams met 28 times when Leeds were relegated from the Premier League. The rivalry began in League One during the 2007–08 season, with disorder and violent clashes between both sets of fans and the police at Elland Road. It continued into the 2008–09 season; where the teams were vying for promotion to the Championship, culminating in Millwall knocking Leeds out of the League One playoffs at the semi-final stage.

The rivalry between the teams is intensified by both clubs' passionate fans and association with football hooliganism. The clubs' two hooligan firms; the Leeds United Service Crew and the Millwall Bushwackers were notorious in the 1970s and 80s for their violence, being called "dirty Leeds" and "the scourge of football" respectively. Leeds and Millwall are two of the most hated clubs in British football, with supporters of other teams still attaching a stigma of trouble to the clubs and their fans. As a result of fighting and disorder between supporters in 2007, kick-off times in future fixtures between the sides were made earlier and matches heavily policed at The Den by the Metropolitan Police and at Elland Road by the West Yorkshire Police. An 'anti-hooligan operation' was introduced by West Yorkshire Police in 2010 for Millwall fans to exchange vouchers for tickets at Woolley Edge service station, severely limiting the number of supporters attending away games at Elland Road. Despite heavier policing measures, there has still been numerous incidents in fixtures; including racial chanting and abuse of players, tragedy chanting from supporters mocking the death of fans, and assault on a player by a fan who entered the field of play.

According to a survey conducted during the 2012–13 season, Leeds fans consider Millwall to be their joint-third biggest rival along with West Yorkshire side Huddersfield Town. Millwall's main rival is fellow London club West Ham United. The clubs have played each other 45 times and are almost evenly matched. Both teams have won 20, with five games drawn and both sides being dominant at home. As of the 2024–25 season, both teams play in the Championship. The clubs have competed in different divisions for the best part of their 98 seasons in the Football League, and have spent twenty seasons together in the same tier.