Head professor retiring, led out (6)
I believe the answer is:
noddle
'head' is the definition.
(noddle is a kind of head)
'professor retiring led out' is the wordplay.
'professor' becomes 'don' (I've seen this before).
'retiring' is a reversal indicator.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'don' written backwards gives 'nod'.
'led' with letters rearranged gives 'dle'.
'nod'+'dle'='NODDLE'
(Other definitions for noddle that I've seen before include "Jocular word for head" , "Bonce" , "Head (sl.)" , "Head or brain (slang)" .)