Short summary concerning headgear (5)
I believe the answer is:
recap
'short summary' is the definition.
(I've seen this in another clue)
'concerning headgear' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'headgear' becomes 'cap' (cap is a kind of headgear).
're'+'cap'='RECAP'
(Other definitions for recap that I've seen before include "Summary of main points" , "Go over old ground" , "Quickly run through" , "In summary, state again" , "Summarise briefly (abbr)" .)