Stroke, not the first that hurts (4)
I believe the answer is:
ouch
'that hurts' is the definition.
'stroke not the first' is the wordplay.
'stroke' becomes 'touch'.
'not the first' means to remove the first letter.
'touch' with its first letter taken off is 'OUCH'.
(Other definitions for ouch that I've seen before include "Cry of pain" , "Exclamation of pain - that hurt!" , "Pained exclamation" , "Pained cry" , "Exclamation of sudden pain" .)