Agonising hard over stick for shooting in golf (9)
I believe the answer is:
harrowing
'agonising' is the definition.
(I know that agonising can be written as harrowing)
'hard over stick for shooting in golf' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'over' says to put letters next to each other.
'stick for shooting' becomes 'arrow' (stick shot through the air).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'h'+'arrow'+'in'+'g'='HARROWING'
(Other definitions for harrowing that I've seen before include "work for a farmer" , "Breaking new ground" , "stressful" , "Acutely distressing" , "traumatic" .)