For city of Leipzig, former East German teams VfB/Lokomotive Leipzig and Chemie still exist in the lower divisions.
Lokomotive's Wikipedia: "The club's fans share a fierce and often violent rivalry with the supporters of
Chemie Leipzig. When both teams met in the quarter finals of the
Sachsenpokal in 2016, German daily newspaper
Die Welt called the match the "German
hooligan summit".
[8] An additional reason for the enmity between some fan groups (namely their
ultras) is a political one. Whereas certain Chemie fan clubs express
left-wing and
anti-fascist political views, Lok has vocal supporters from the
right and
far-right of the political spectrum"
Don't remember anything from Chemie, but I do remember Lokomotiv's Cup Winners Cup final against Ajax, which was Marco van Basten's emerging on the international stage before his moving to Milan for his glory days.