Fencer's thrust one support piercing uncovered area (7)
I believe the answer is:
riposte
'fencer's thrust' is the definition.
(I've seen this in another clue)
'one support piercing uncovered area' is the wordplay.
'one' becomes 'i' (Roman numeral).
'support' becomes 'post' (post is a kind of support).
'piercing' means one lot of letters goes inside another (some letters pierce a hole in others).
'uncovered' says to take the centre.
The central letters of 'area' are 're'.
'i'+'post'='ipost'
'ipost' put into 're' is 'RIPOSTE'.
(Other definitions for riposte that I've seen before include "Quick and witty reply" , "Sally" , "Rejoinder" , "Quick sharp reply" , "Repartee; quick thrust (fencing)" .)