Stray sheep going round the ring (4)
I believe the answer is:
roam
'stray' is the definition.
('roam' can be a synonym of 'stray')
'sheep going round the ring' is the wordplay.
'sheep' becomes 'ram' (ram is a kind of sheep).
'going round' means one lot of letters goes inside another.
'the ring' becomes 'o'.
'ram' going around 'o' is 'ROAM'.
(Other definitions for roam that I've seen before include "Walk without a specific destination" , "Wander freely" , "Rove or ramble" , "Peregrinate" , "Wander about aimlessly" .)