Snotball is in part 3 of the original Enemy Within Campaign, "The Power Behind the Throne", or rather it's in the "Warhammer City" sourcebook afiliated with that adventure. I think was intended to be basically football(soccer) with a trussed-up snotling instead of a ball, or maybe it was rugby. I think they drug the snotling so that it doesn't bite anyone.
Blood Bowl doesn't quite fit in the standard WFRP world, but it wouldn't be too hard to make a career. Careers are pretty easy to make up, just find something a bit similar and tweak it until it feels right. Then give a special ability- something regarding unarmed combat would make sense. Stats might vary depending on position between S,T and A.