Stunner modelled again, having retired (5)
I believe the answer is:
taser
'stunner' is the definition.
(I've seen this before)
'modelled again having retired' is the wordplay.
'modelled again' becomes 'resat' ('sat' can be a synonym for 'modelled' so perhaps 'resat' is OK for 'modelled again').
'having retired' says the letters should be written backwards.
'resat' in reverse letter order is 'TASER'.
(Other definitions for taser that I've seen before include "Weapon used to deliver a temporarily paralysing electric shock" , "Police stun weapon" , "PC kit" , "Device used to stun someone temporarily" , "The weapon delivers a temporary paralysing electric shock" .)