Outside ring, smell a trap (5)
I believe the answer is:
noose
'a trap' is the definition.
(noose is a kind of trap)
'outside ring smell' is the wordplay.
'outside' is an insertion indicator.
'ring' becomes 'o' (**).
'smell' becomes 'nose' (nose is a kind of smell).
'o' inserted within 'nose' is 'NOOSE'.
(Other definitions for noose that I've seen before include "Device for capital punishment" , "Hanging material" , "Looped rope" , "Bond" , "form of punishment" .)