the top club in Hannover is the
DRC Hannover, which plays in the 1st Bundesliga. There are no "official" Touch rugby clubs, ie none that belong to the German touch federation but if you fancy helping to start off some grass roots touch, let me know and we can help organise some training sessions. I am sure the Berliners would be happy to help you along.
Here are all the Rugby Union clubs in Hannover:
Hannover, DRC Hannover, DSV 78 Hannover, FC Schwalbe Beschreibung: Rugbyabteilung des FCSchwalbe dreifacher deutscher Rugbymeister
Hannover, SV Odin Beschreibung: Sportverein Odin Hannover von 1905 e. V.