Bubble football! It's not unique to Berlin, but it seems to be popular in Berlin and it fits the bill: it's physically demanding, absurdly fun (also, absurdly absurd), different, and probably suits someone called "soccerman"
Image search explains the idea better than I could: (also, there are lots of great videos, here's one).
There are lots of results for it in Berlin. Looks like it's also known as Bubble Footbälle, Loopybälle and Bubble Fußbälle in German. I've only played it in London so can't vouch for individual companies.
Some tips from my experience:
- It really is as much fun as it looks
- It's more tiring and physically demanding than it looks! Those things get hot and heavy. I recommend short games, short bursts, take breaks. It's most fun when you've got the energy to charge your friends full speed, head first, and see who can stay upright!
- If you take it seriously it does work as a competitive sport (there are actual leagues), and you can come up with all sorts of creative strategies (my personal favourite was having teammates charge down the opponents while lobbing the actual football over all of their heads while they were distracted). It's also lots of fun when you forget the goals for a while and just bounce around or do stunts. I recommend a mix of the two!
- You end up upside-down, a lot. Don't eat or drink too much before! Sometimes you get stuck perfectly upside down with your legs waving in the air like an upturned beetle - you can right yourself, but it's not easy (or wriggle out, but that's less fun).
- Your upper half (including head) is extremely well protected, but your ankles will hit the ground at speed, often... if you're not limping for about an hour afterwards, you weren't playing hard enough