Stroke, not the first that hurts (4)
I believe the answer is:
Here is my best explanation:
'that hurts' is the definition.
'stroke not the first' is the subsidiary indication.
'stroke' becomes 'touch'.
'not the first' means to remove the first letter.
'touch' with its initial letter taken off is 'ouch'.
(Other definitions for ouch that I've seen before include "That hurt!", "I hurt", "Pained cry", "cry of pain", "Exclamation of sudden pain", "response to a bad pun", "sounds painful", "shout of pain", "Shout of pain" and "Cry of pain".)