Celtic vs Rangers (Old Firm)

The most violent rivalry in world football. The Old Firm is rooted in the Catholic-Protestant sectarian divide in Glasgow — Celtic represents the Irish Catholic community, Rangers the Protestant establishment. The rivalry has been linked to murders, riots, and domestic violence spikes (reports increase 200% on Old Firm days). Over 100 arrests per match are common. It's also the most passionate: 50,000 fans sing for 90 minutes nonstop. The clubs have won 107 Scottish league titles combined (out of 125). Rangers' 2012 liquidation and relegation to the fourth division — then march back up to the Premiership — only intensified the hatred.