Reasonable European supports Spain intermittently (4)
I believe the answer is:
sane
'reasonable' is the definition.
('sane' can be similar in meaning to 'reasonable')
'european supports spain intermittently' is the wordplay.
'european' becomes 'e' (abbreviation e.g. EU).
'supports' says to put letters next to each other (bottom letters provide a support for the top ones).
'intermittently' means one should take alternating letters.
The alternating letters of 'spain' are 'san'.
'e' put after 'san' is 'SANE'.
(Other definitions for sane that I've seen before include "Right-minded" , "Mentally sound" , "Not mad" , "Identical" , "Compos mentis" .)