I am a Reserve, and to simplify it consists in a sport where the players fly on magic brooms. The goal posts are up high, there is a magic flying ball that will guarantee your team's win if it is caught (which is extremely hard so there is a player specifically for that purpose), chasers try to score against their adversary, keepers try to keep the chasers from scoring and beaters defend their teammates against these other magic balls that are meant to hit and disrupt them (violently, I might add).