Harmony left following musical style (7)
I believe the answer is:
rapport
'harmony' is the definition.
(rapport is a kind of harmony)
'left following musical style' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'following' means one lot of letters go next to another.
'musical style' becomes 'rap' (music genre).
'port' put after 'rap' is 'RAPPORT'.
(Other definitions for rapport that I've seen before include "communion" , "Feeling of affinity and harmony" , "Feeling of sympathy and understanding" , "Emotional bond" , "Harmonious understanding with someone" .)