Head scratched, contact that hurt! (4)
I believe the answer is:
ouch
'that hurt' is the definition.
(I've seen this before)
'head scratched contact' is the wordplay.
'head scratched' means to remove the first letter.
'contact' becomes 'touch' (touch is a kind of contact).
'touch' with its initial letter taken away is 'OUCH'.
(Other definitions for ouch that I've seen before include "that hurts!" , "Ow!" , "that's painful" , "Reaction when pricked" , "Exclamation of sudden pain" .)