This is where our (well one of them) local rugby club gets their gear.
Niebel KG
Dossenheimer Landstraße 98
69121 Heidelberg
http://www.niebel-mode.de/index.html
From the Hauptbahnhof you get Strassenbahn 1 to Handschuhsheim, get off at Bahnhof OEG. Or Strassenbahn 4 to Handschuhsheim, & get off at Burgstr. It's about a 5 min walk from either stop.
If you go to the shop website (above) they have a map of where the shop is.
Hope this helps