Helen's lover is below average (5)
I believe the answer is:
'helen's lover' is the definition.
(I've seen this in another clue)
'is below average' is the wordplay.
'below' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'average' becomes 'par' (average score in golf).
'is' after 'par' is 'PARIS'.
(Other definitions for paris that I've seen before include "Helen's abductor" , "European capital - Greek hero" , "foreign city" , "City on the Seine" , "City where one may see the Mona Lisa" .)