Brain in head's spinning (4)
I believe the answer is:
stun
'brain' is the definition.
The answer and definition can be both to do with contact as well as being verbs in their base form.
Maybe there's a link between them I don't understand?
'head's spinning' is the wordplay.
'head's' becomes 'nut's' (informal term for somebody's head).
'spinning' is a reversal indicator.
'nuts' back-to-front is 'STUN'.
'in' is the link.
Can you help me to learn more?
(Other definitions for stun that I've seen before include "Knock out temporarily" , "Leave speechless" , "Shock, flabbergast" , "Daze, knock senseless" , "Daze with nuts" .)