It catches the back part (4)
I believe the answer is:
trap
'it catches' is the definition.
The definition suggests a singular noun which matches the answer.
'back part' is the wordplay.
'back' is a reversal indicator.
'part' in reverse letter order is 'TRAP'.
'the' is the link.
Can you help me to learn more?
(Other definitions for trap that I've seen before include "Trick" , "Snaring device" , "Light carriage - it's sometimes sprung!" , "that may be sprung?" , "Means of transport (sometime sprung!)" .)