Dusseldorf was very good when I went on a stag there earlier this year. Would easily be able to get tickets for their games too as they're in the second tier. But if you're in that sort of area, as people above have said, there's tons of places within an hour on the train. I don't think you'd have many issues with a decent sized group in Dusseldorf, Hamburg or Koln.
I've been to Stuttgart & Munich too and that was a little more difficult, particularly Munich.