Trauma-resistant old academic goes about with untidy mass of hair (10)
I believe the answer is:
shockproof
'trauma-resistant' is the definition.
'old academic goes about with untidy mass of hair' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'academic' becomes 'prof'.
'goes about' indicates putting letters inside.
'with' is a charade indicator (letters next to each other).
'untidy mass of hair' becomes 'shock' (shock can mean an unkempt mass of hair).
'o' inserted into 'prof' is 'proof'.
'proof' after 'shock' is 'SHOCKPROOF'.
(Other definitions for shockproof that I've seen before include "Resistant to impact" , "Unshakeable" .)