Gets half loopy over a girl (5)
I believe the answer is:
madge
'a girl' is the definition.
'gets half loopy over' is the wordplay.
'half' means to take half the letters.
'loopy' becomes 'mad' (I've seen this in another clue).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'gets' cut in half is 'ge'.
'ge' put after 'mad' is 'MADGE'.
(Other definitions for madge that I've seen before include "girl" , "Madonna's nickname" .)