Rodolphus Lestrange is known for having secret (and also illegal) duels in the undergrounds of hogwarts. There have been several incidents, but fortunately, nothing is too serious.. only thanks to you. Some friends of yours from Slytherin participate in these duels, and you decided to come too, but to help in case someone gets hurt. So now you are basically the healer for all these duels. You also stop them when it gets too dangerous. Rodolphus may have caught some interest in you.