The Spanish inside fail to hit on a girl (7)
I believe the answer is:
melissa
'girl' is the definition.
'the spanish inside fail to hit on a' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'inside' indicates putting letters inside.
'fail to hit' becomes 'miss' (I've seen this before).
'on' means one lot of letters go next to another.
'el' placed into 'miss' is 'meliss'.
'meliss'+'a'='MELISSA'
(Other definitions for melissa that I've seen before include "Female" , "woman" , "Girl's name meaning "bee"" .)