Concern over pitfall (4)
I believe the answer is:
trap
'pitfall' is the definition.
(I've seen this in another clue)
'concern over' is the wordplay.
'concern' becomes 'part' (part is a kind of concern).
'over' says the letters should be written in reverse.
'part' back-to-front is 'TRAP'.
(Other definitions for trap that I've seen before include "Snare; light carriage" , "Lure, snare" , "Light horse-drawn carriage" , "Light carriage - it's sometimes sprung!" , "Bunker; carriage" .)