Row stifles stray dog (7)
I believe the answer is:
terrier
'dog' is the definition.
(terrier is a kind of dog)
'row stifles stray' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'stifles' means one lot of letters goes inside another.
'stray' becomes 'err' (to err is to stray or go wrong).
'tier' placed around 'err' is 'TERRIER'.
(Other definitions for terrier that I've seen before include "Dog - old land register" , "One who volunteers to fight" , "Small, short-bodied dog" , "Small hunting dog" , "Dog - army volunteer - land register" .)