I saw Hyeon Chung (briefly) play in DC last week against Cilic. IMO, Chung hasn't fully matured into his body - he's still pretty thin but doesn't appear to have a true ectomorph body build. Like Nick Kyrgios, if you look at his pictures from when he was a younger player, Chung was kind of short and chubby. IF Chung isn't done growing (i.e. he fills out), he'll likely become a much stronger (literally and figuratively) and more dangerous player.