Back part is a snare (4)
I believe the answer is:
trap
'snare' is the definition.
(I know that snare can be written as trap)
'back part' is the wordplay.
'back' is a reversal indicator.
'part' back-to-front is 'TRAP'.
'is a' is the link.
(Other definitions for trap that I've seen before include "that can let an actor down" , "Golfing hazard" , "one would be ill advised to enter?" , "corner" , "It commonly has a role in speaking" .)