Fussy digger starting to yawn (5)
I believe the answer is:
picky
'fussy' is the definition.
(I know that fussy can be written as picky)
'digger starting to yawn' is the wordplay.
'digger' becomes 'pick' (tool used when digging).
'starting to' says to take the initial letters.
The first letter of 'yawn' is 'y'.
'pick'+'y'='PICKY'
(Other definitions for picky that I've seen before include "Choosy" , "Finicky" , "Excessively particular" , "Discriminating" , "Excessively fastidious" .)