An asset in terms of sponsoring can be defined as a (valuable) client of a marketer - for an example an individual athlete or a club. It does not matter wheter or not the marketer owns exclusive rights for the client.
Sponsoo has close to 5.000 registered Users on the platform (September 2016) - meaning that Sponsoo represents 5.000 assets. That makes Sponsoo, ranked by the number of assets, the biggest sport-marketer in Germany. The word "asset" represents the appreciation Sponsoo has for its clients very well. Loosely translated into German, "asset" means as much as "valuable item".