Prince Sebastien plays rugby on Luxembourgs U19 National Rugby Team. Apparently, he plays very well. He has a normal relationship with his teammates and they occasionally enjoy teasing him about his royal status. He pointedly said to the press who were part of the coverage of the team that he did not want to be treated any different than his teammates.
This was mentioned in Wort a while back when his team played Croatia. The team hosted some press recently so Seb's participation on the rugby team made the covers of several magazines Promi, Revue, et al. Promi has changed their cover already and the article was not available online. You may read the Revue article online.