Sentimental sports supporter keeping wicket (4)
I believe the answer is:
twee
'sentimental' is the definition.
(I've seen this before)
'sports supporter keeping wicket' is the wordplay.
'sports supporter' becomes 'tee' (a tee supports a golf ball).
'keeping' indicates putting letters inside.
'wicket' becomes 'w'.
'tee' placed around 'w' is 'TWEE'.
(Other definitions for twee that I've seen before include "Small and pretty" , "Affectedly dainty or refined" , "Precious - sentimental" , "Over-pretty, sentimental" , "Affectedly pretty" .)